r"""
Elements of graded rings of modular forms for Hecke triangle groups

AUTHORS:

- Jonas Jermann (2013): initial version

"""
from __future__ import absolute_import

#*****************************************************************************
#       Copyright (C) 2013-2014 Jonas Jermann <jjermann2@gmail.com>
#
#  Distributed under the terms of the GNU General Public License (GPL)
#  as published by the Free Software Foundation; either version 2 of
#  the License, or (at your option) any later version.
#                  http://www.gnu.org/licenses/
#*****************************************************************************

from sage.misc import six
from sage.rings.all import ZZ, infinity, LaurentSeries, O
from sage.functions.all import exp
from sage.rings.number_field.number_field import QuadraticField
from sage.symbolic.all import pi

from sage.structure.parent_gens import localvars
from sage.structure.richcmp import op_NE, op_EQ
from sage.structure.element import CommutativeAlgebraElement
from sage.structure.unique_representation import UniqueRepresentation

from sage.modules.free_module_element import vector
from sage.geometry.hyperbolic_space.hyperbolic_interface import HyperbolicPlane

from sage.misc.cachefunc import cached_method
from sage.misc.inherit_comparison import InheritComparisonClasscallMetaclass

from .constructor import rational_type, FormsSpace, FormsRing
from .series_constructor import MFSeriesConstructor


# Warning: We choose CommutativeAlgebraElement because we want the
# corresponding operations (e.g. __pow__) even though the category
# (and class) of the parent is in some cases not
# CommutativeAlgebras but Modules
class FormsRingElement(six.with_metaclass(
        InheritComparisonClasscallMetaclass,
        CommutativeAlgebraElement, UniqueRepresentation
    )):
    r"""
    Element of a FormsRing.
    """
    from .analytic_type import AnalyticType
    AT = AnalyticType()

    @staticmethod
    def __classcall__(cls, parent, rat):
        r"""
        Return a (cached) instance with canonical parameters.

        EXAMPLES::

            sage: from sage.modular.modform_hecketriangle.graded_ring_element import FormsRingElement
            sage: from sage.modular.modform_hecketriangle.graded_ring import ModularFormsRing
            sage: (x,d) = var("x","d")
            sage: el = FormsRingElement(ModularFormsRing(), x*d)
            sage: el.rat()
            x*d
            sage: el.rat().parent()
            Fraction Field of Multivariate Polynomial Ring in x, y, z, d over Integer Ring
        """

        rat = parent.rat_field()(rat)
        # rat.reduce() <- maybe add this for the nonexact case

        return super(FormsRingElement,cls).__classcall__(cls, parent, rat)

    def __init__(self, parent, rat):
        r"""
        Element of a FormsRing ``parent`` corresponding to the rational
        function ``rat`` evaluated at ``x=f_rho``, ``y=f_i``, ``z=E2``
        and ``d`` by the formal parameter from ``parent.coeff_ring()``.

        The functions ``f_rho, f_i, E2`` can be obtained from
        ``self.parent().graded_ring()``.

        .. NOTE::

            If ``n=Infinity`` then the variable ``x`` refers to ``E4`` instead
            of ``f_rho=1``.

        INPUT:

        - ``parent`` -- An (non abstract) instance of ``FormsRing_abstract``.

        - ``rat``    -- A rational function in ``parent.rat_field()``, the
                        fraction field of the polynomial ring in ``x,y,z,d``
                        over the base ring of ``parent``.

        OUTPUT:

        An element of ``parent``. If ``rat`` does not correspond to such
        an element an exception is raised.

        EXAMPLES::

            sage: from sage.modular.modform_hecketriangle.graded_ring import QuasiModularFormsRing
            sage: (x,y,z,d)=var("x,y,z,d")
            sage: MR = QuasiModularFormsRing(n=5)
            sage: el = MR(x^3*d + y*z)
            sage: el
            f_rho^3*d + f_i*E2
            sage: el.rat()
            x^3*d + y*z
            sage: el.parent()
            QuasiModularFormsRing(n=5) over Integer Ring
            sage: el.rat().parent()
            Fraction Field of Multivariate Polynomial Ring in x, y, z, d over Integer Ring

            sage: MR = QuasiModularFormsRing(n=infinity)
            sage: el = MR(d*x*(x-y^2))
            sage: el
            -E4*f_i^2*d + E4^2*d
            sage: el.rat()
            -x*y^2*d + x^2*d
            sage: el.parent()
            QuasiModularFormsRing(n=+Infinity) over Integer Ring
        """

        self._rat = rat
        (elem, homo, self._weight, self._ep, self._analytic_type) = rational_type(rat, parent.hecke_n(), parent.base_ring())

        if not (
            elem and\
            self._analytic_type <= parent.analytic_type() ):
                raise ValueError("{} does not correspond to an element of the {}.".format(rat, parent))

        super(FormsRingElement, self).__init__(parent)

    # Unfortunately the polynomial ring does not give unique
    # representations of elements (with respect to ==)
    def _richcmp_(self, other, op):
        r"""
        Return whether ``self`` is equal to ``other``.

        They are considered equal if the corresponding rational
        functions are equal and the groups match up.

        EXAMPLES::

            sage: from sage.modular.modform_hecketriangle.graded_ring import MeromorphicModularFormsRing
            sage: (x,y,z,d) = MeromorphicModularFormsRing().pol_ring().gens()
            sage: MeromorphicModularFormsRing(n=3)(x) == MeromorphicModularFormsRing(n=4)(x)
            False
            sage: MeromorphicModularFormsRing()(-1/x) is MeromorphicModularFormsRing()(1/(-x))
            False
            sage: MeromorphicModularFormsRing()(-1/x) == MeromorphicModularFormsRing()(1/(-x))
            True
            sage: MeromorphicModularFormsRing(base_ring=CC)(-1/x) == MeromorphicModularFormsRing()(1/(-x))
            True
        """
        if op not in [op_EQ, op_NE]:
            return NotImplemented

        if self.group() == other.group():
            if self.group().is_arithmetic():
                b = (self.rat().subs(d=self.group().dvalue()) ==
                     other.rat().subs(d=other.group().dvalue()))
            else:
                b = (self.rat() == other.rat())

        return b == (op == op_EQ)

    def _repr_(self):
        r"""
        Return the string representation of ``self``.

        EXAMPLES::

            sage: from sage.modular.modform_hecketriangle.graded_ring import QuasiModularFormsRing
            sage: (x,y,z,d)=var("x,y,z,d")
            sage: QuasiModularFormsRing(n=5)(x^3*z-d*y)
            f_rho^3*E2 - f_i*d

            sage: QuasiModularFormsRing(n=infinity)(x)
            E4
        """

        return self._rat_repr()

    def _rat_repr(self):
        r"""
        Return a string representation of ``self`` as a rational function in the generators.

        EXAMPLES::

            sage: from sage.modular.modform_hecketriangle.space import QuasiModularForms
            sage: (x,y,z,d)=var("x,y,z,d")
            sage: QuasiModularForms(n=5, k=6, ep=-1)(x^3*z)._rat_repr()
            'f_rho^3*E2'

            sage: QuasiModularForms(n=infinity, k=10)(x*(x-y^2)*z)._rat_repr()
            '-E4*f_i^2*E2 + E4^2*E2'
        """

        if (self.hecke_n() == infinity):
            with localvars(self.parent()._pol_ring, "E4, f_i, E2, d"):
                pol_str = str(self._rat)
        else:
            with localvars(self.parent()._pol_ring, "f_rho, f_i, E2, d"):
                pol_str = str(self._rat)

        return "{}".format(pol_str)

    def _qexp_repr(self):
        r"""
        Return a string representation of ``self`` as a Fourier series.

        EXAMPLES::

            sage: from sage.modular.modform_hecketriangle.graded_ring import QuasiModularFormsRing
            sage: (x,y,z,d)=var("x,y,z,d")
            sage: MR = QuasiModularFormsRing(n=5)
            sage: MR.disp_prec(3)
            sage: MR(x^3*z-d*y)._qexp_repr()
            '-d + 1 + ((65*d + 33)/(200*d))*q + ((1755*d + 1437)/(320000*d^2))*q^2 + O(q^3)'

            sage: QuasiModularFormsRing(n=infinity)(x*(x-y^2)*z)._qexp_repr()
            '64*q - 3840*q^3 - 16384*q^4 + O(q^5)'
        """

        # For now the series constructor doesn't behave well for non exact bases... :(
        if (self.group().is_arithmetic() or not self.base_ring().is_exact()):
            return str(self.q_expansion_fixed_d().add_bigoh(self.parent()._disp_prec))
        else:
            return str(self.q_expansion().add_bigoh(self.parent()._disp_prec))

    def _latex_(self):
        r"""
        Return the LaTeX representation of ``self``.

        EXAMPLES::

            sage: from sage.modular.modform_hecketriangle.graded_ring import QuasiModularFormsRing
            sage: (x,y,z,d)=var("x,y,z,d")
            sage: latex(QuasiModularFormsRing(n=5)(x^3*z-d*y))
            f_{\rho}^{3} E_{2} -  f_{i} d

            sage: from sage.modular.modform_hecketriangle.space import CuspForms
            sage: latex(CuspForms(k=12)(x^3-y^2))
            f_{\rho}^{3} -  f_{i}^{2}

            sage: latex(QuasiModularFormsRing(n=infinity)(x*(x-y^2)*z))
            - E_{4} f_{i}^{2} E_{2} + E_{4}^{2} E_{2}
        """

        from sage.misc.latex import latex

        if (self.hecke_n() == infinity):
            with localvars(self.parent()._pol_ring, "E4, f_i, E2, d"):
                latex_str = latex(self._rat)
        else:
            with localvars(self.parent()._pol_ring, "f_rho, f_i, E2, d"):
                latex_str = latex(self._rat)

        return latex_str

    def group(self):
        r"""
        Return the (Hecke triangle) group of ``self.parent()``.

        EXAMPLES::

            sage: from sage.modular.modform_hecketriangle.space import ModularForms
            sage: ModularForms(n=12, k=4).E4().group()
            Hecke triangle group for n = 12
        """

        return self.parent().group()

    def hecke_n(self):
        r"""
        Return the parameter ``n`` of the (Hecke triangle) group of ``self.parent()``.

        EXAMPLES::

            sage: from sage.modular.modform_hecketriangle.space import ModularForms
            sage: ModularForms(n=12, k=6).E6().hecke_n()
            12
        """

        return self.parent().hecke_n()

    def base_ring(self):
        r"""
        Return base ring of ``self.parent()``.

        EXAMPLES::

            sage: from sage.modular.modform_hecketriangle.space import ModularForms
            sage: ModularForms(n=12, k=4, base_ring=CC).E4().base_ring()
            Complex Field with 53 bits of precision
        """

        return self.parent().base_ring()

    def coeff_ring(self):
        r"""
        Return coefficient ring of ``self``.

        EXAMPLES::

            sage: from sage.modular.modform_hecketriangle.graded_ring import ModularFormsRing
            sage: ModularFormsRing().E6().coeff_ring()
            Fraction Field of Univariate Polynomial Ring in d over Integer Ring
        """

        return self.parent().coeff_ring()

    def rat(self):
        r"""
        Return the rational function representing ``self``.

        EXAMPLES::

            sage: from sage.modular.modform_hecketriangle.graded_ring import ModularFormsRing
            sage: ModularFormsRing(n=12).Delta().rat()
            x^30*d - x^18*y^2*d
        """

        return self._rat

    def _reduce_d(self):
        r"""
        Return a new version of ``self`` where `d` is replaced by its value in
        the presentation of ``self`` as a rational function in the polynomial generators.

        The new element still compares equal to the old one but the corresponding
        rational function no longer contains any ``d`` (in the arithmetic cases).

        EXAMPLES::

            sage: from sage.modular.modform_hecketriangle.space import ModularForms, WeakModularForms
            sage: Delta = ModularForms().Delta()
            sage: Delta.rat()
            x^3*d - y^2*d
            sage: Delta2 = Delta._reduce_d()
            sage: Delta2.rat()
            (x^3 - y^2)/1728
            sage: Delta == Delta2
            True
        """

        if not self.group().is_arithmetic():
            return self

        d = self.parent().get_d(fix_d=True)
        return self.parent()(self._rat.subs(d=d))

    def is_homogeneous(self):
        r"""
        Return whether ``self`` is homogeneous.

        EXAMPLES::

            sage: from sage.modular.modform_hecketriangle.graded_ring import QuasiModularFormsRing
            sage: QuasiModularFormsRing(n=12).Delta().is_homogeneous()
            True
            sage: QuasiModularFormsRing(n=12).Delta().parent().is_homogeneous()
            False
            sage: x,y,z,d=var("x,y,z,d")
            sage: QuasiModularFormsRing(n=12)(x^3+y^2+z+d).is_homogeneous()
            False

            sage: QuasiModularFormsRing(n=infinity)(x*(x-y^2)+y^4).is_homogeneous()
            True
        """

        return self._weight != None

    def weight(self):
        r"""
        Return the weight of ``self``.

        EXAMPLES::

            sage: from sage.modular.modform_hecketriangle.graded_ring import QuasiModularFormsRing
            sage: from sage.modular.modform_hecketriangle.space import ModularForms
            sage: x,y,z,d = var("x,y,z,d")
            sage: QuasiModularFormsRing()(x+y).weight() is None
            True
            sage: ModularForms(n=18).f_i().weight()
            9/4
            sage: ModularForms(n=infinity).f_inf().weight()
            4
        """

        return self._weight

    def ep(self):
        r"""
        Return the multiplier of ``self``.

        EXAMPLES::

            sage: from sage.modular.modform_hecketriangle.graded_ring import QuasiModularFormsRing
            sage: from sage.modular.modform_hecketriangle.space import ModularForms
            sage: x,y,z,d = var("x,y,z,d")
            sage: QuasiModularFormsRing()(x+y).ep() is None
            True
            sage: ModularForms(n=18).f_i().ep()
            -1
            sage: ModularForms(n=infinity).E2().ep()
            -1
        """

        return self._ep

    def degree(self):
        r"""
        Return the degree of ``self`` in the graded ring.
        If ``self`` is not homogeneous, then ``(None, None)``
        is returned.

        EXAMPLES::

            sage: from sage.modular.modform_hecketriangle.graded_ring import QuasiModularFormsRing
            sage: from sage.modular.modform_hecketriangle.space import ModularForms
            sage: x,y,z,d = var("x,y,z,d")
            sage: QuasiModularFormsRing()(x+y).degree() == (None, None)
            True
            sage: ModularForms(n=18).f_i().degree()
            (9/4, -1)
            sage: ModularForms(n=infinity).f_rho().degree()
            (0, 1)
        """

        return (self._weight,self._ep)

    def is_modular(self):
        r"""
        Return whether ``self`` (resp. its homogeneous components)
        transform like modular forms.

        EXAMPLES::

            sage: from sage.modular.modform_hecketriangle.graded_ring import QuasiModularFormsRing
            sage: from sage.modular.modform_hecketriangle.space import QuasiModularForms
            sage: x,y,z,d = var("x,y,z,d")
            sage: QuasiModularFormsRing(n=5)(x^2+y-d).is_modular()
            True
            sage: QuasiModularFormsRing(n=5)(x^2+y-d+z).is_modular()
            False
            sage: QuasiModularForms(n=18).f_i().is_modular()
            True
            sage: QuasiModularForms(n=18).E2().is_modular()
            False
            sage: QuasiModularForms(n=infinity).f_inf().is_modular()
            True
        """

        return not (self.AT("quasi") <= self._analytic_type)

    def is_weakly_holomorphic(self):
        r"""
        Return whether ``self`` is weakly holomorphic
        in the sense that: ``self`` has at most a power of ``f_inf``
        in its denominator.

        EXAMPLES::

            sage: from sage.modular.modform_hecketriangle.graded_ring import QuasiMeromorphicModularFormsRing
            sage: from sage.modular.modform_hecketriangle.space import QuasiMeromorphicModularForms
            sage: x,y,z,d = var("x,y,z,d")
            sage: QuasiMeromorphicModularFormsRing(n=5)(x/(x^5-y^2)+z).is_weakly_holomorphic()
            True
            sage: QuasiMeromorphicModularFormsRing(n=5)(x^2+y/x-d).is_weakly_holomorphic()
            False
            sage: QuasiMeromorphicModularForms(n=18).J_inv().is_weakly_holomorphic()
            True
            sage: QuasiMeromorphicModularForms(n=infinity, k=-4)(1/x).is_weakly_holomorphic()
            True
            sage: QuasiMeromorphicModularForms(n=infinity, k=-2)(1/y).is_weakly_holomorphic()
            False
        """

        return self.AT("weak", "quasi") >= self._analytic_type

    def is_holomorphic(self):
        r"""
        Return whether ``self`` is holomorphic
        in the sense that the denominator of ``self``
        is constant.

        EXAMPLES::

            sage: from sage.modular.modform_hecketriangle.graded_ring import QuasiMeromorphicModularFormsRing
            sage: from sage.modular.modform_hecketriangle.space import QuasiMeromorphicModularForms
            sage: x,y,z,d = var("x,y,z,d")
            sage: QuasiMeromorphicModularFormsRing(n=5)((y^3-z^5)/(x^5-y^2)+y-d).is_holomorphic()
            False
            sage: QuasiMeromorphicModularFormsRing(n=5)(x^2+y-d+z).is_holomorphic()
            True
            sage: QuasiMeromorphicModularForms(n=18).J_inv().is_holomorphic()
            False
            sage: QuasiMeromorphicModularForms(n=18).f_i().is_holomorphic()
            True
            sage: QuasiMeromorphicModularForms(n=infinity).f_inf().is_holomorphic()
            True
        """

        return self.AT("holo", "quasi") >= self._analytic_type

    def is_cuspidal(self):
        r"""
        Return whether ``self`` is cuspidal
        in the sense that ``self`` is holomorphic and ``f_inf``
        divides the numerator.

        EXAMPLES::

            sage: from sage.modular.modform_hecketriangle.graded_ring import QuasiModularFormsRing
            sage: from sage.modular.modform_hecketriangle.space import QuasiModularForms
            sage: x,y,z,d = var("x,y,z,d")
            sage: QuasiModularFormsRing(n=5)(y^3-z^5).is_cuspidal()
            False
            sage: QuasiModularFormsRing(n=5)(z*x^5-z*y^2).is_cuspidal()
            True
            sage: QuasiModularForms(n=18).Delta().is_cuspidal()
            True
            sage: QuasiModularForms(n=18).f_rho().is_cuspidal()
            False
            sage: QuasiModularForms(n=infinity).f_inf().is_cuspidal()
            False
            sage: QuasiModularForms(n=infinity).Delta().is_cuspidal()
            True
        """
        return self.AT("cusp", "quasi") >= self._analytic_type

    def is_zero(self):
        r"""
        Return whether ``self`` is the zero function.

        EXAMPLES::

            sage: from sage.modular.modform_hecketriangle.graded_ring import QuasiModularFormsRing
            sage: from sage.modular.modform_hecketriangle.space import QuasiModularForms
            sage: x,y,z,d = var("x,y,z,d")
            sage: QuasiModularFormsRing(n=5)(1).is_zero()
            False
            sage: QuasiModularFormsRing(n=5)(0).is_zero()
            True
            sage: QuasiModularForms(n=18).zero().is_zero()
            True
            sage: QuasiModularForms(n=18).Delta().is_zero()
            False
            sage: QuasiModularForms(n=infinity).f_rho().is_zero()
            False
        """
        return self.AT(["quasi"]) >= self._analytic_type

    def analytic_type(self):
        r"""
        Return the analytic type of ``self``.

        EXAMPLES::

            sage: from sage.modular.modform_hecketriangle.graded_ring import QuasiMeromorphicModularFormsRing
            sage: from sage.modular.modform_hecketriangle.space import QuasiMeromorphicModularForms
            sage: x,y,z,d = var("x,y,z,d")
            sage: QuasiMeromorphicModularFormsRing(n=5)(x/z+d).analytic_type()
            quasi meromorphic modular
            sage: QuasiMeromorphicModularFormsRing(n=5)((y^3-z^5)/(x^5-y^2)+y-d).analytic_type()
            quasi weakly holomorphic modular
            sage: QuasiMeromorphicModularFormsRing(n=5)(x^2+y-d).analytic_type()
            modular
            sage: QuasiMeromorphicModularForms(n=18).J_inv().analytic_type()
            weakly holomorphic modular
            sage: QuasiMeromorphicModularForms(n=18).f_inf().analytic_type()
            cuspidal
            sage: QuasiMeromorphicModularForms(n=infinity).f_inf().analytic_type()
            modular
        """
        return self._analytic_type

    def numerator(self):
        r"""
        Return the numerator of ``self``.

        I.e. the (properly reduced) new form corresponding to
        the numerator of ``self.rat()``.

        Note that the parent of ``self`` might (probably will) change.

        EXAMPLES::

            sage: from sage.modular.modform_hecketriangle.graded_ring import QuasiMeromorphicModularFormsRing
            sage: from sage.modular.modform_hecketriangle.space import QuasiMeromorphicModularForms
            sage: x,y,z,d = var("x,y,z,d")
            sage: QuasiMeromorphicModularFormsRing(n=5)((y^3-z^5)/(x^5-y^2)+y-d).numerator()
            f_rho^5*f_i - f_rho^5*d - E2^5 + f_i^2*d
            sage: QuasiMeromorphicModularFormsRing(n=5)((y^3-z^5)/(x^5-y^2)+y-d).numerator().parent()
            QuasiModularFormsRing(n=5) over Integer Ring
            sage: QuasiMeromorphicModularForms(n=5, k=-2, ep=-1)(x/y).numerator()
            1 + 7/(100*d)*q + 21/(160000*d^2)*q^2 + 1043/(192000000*d^3)*q^3 + 45479/(1228800000000*d^4)*q^4 + O(q^5)
            sage: QuasiMeromorphicModularForms(n=5, k=-2, ep=-1)(x/y).numerator().parent()
            QuasiModularForms(n=5, k=4/3, ep=1) over Integer Ring
            sage: (QuasiMeromorphicModularForms(n=infinity, k=-2, ep=-1)(y/x)).numerator()
            1 - 24*q + 24*q^2 - 96*q^3 + 24*q^4 + O(q^5)
            sage: (QuasiMeromorphicModularForms(n=infinity, k=-2, ep=-1)(y/x)).numerator().parent()
            QuasiModularForms(n=+Infinity, k=2, ep=-1) over Integer Ring
        """

        res = self.parent().rat_field()(self._rat.numerator())
        # In general the numerator has a different weight than the original function...
        new_parent = self.parent().extend_type(ring=True).reduce_type(["holo", "quasi"])
        return new_parent(res).reduce()

    def denominator(self):
        r"""
        Return the denominator of ``self``.
        I.e. the (properly reduced) new form corresponding to
        the numerator of ``self.rat()``.

        Note that the parent of ``self`` might (probably will) change.

        EXAMPLES::

            sage: from sage.modular.modform_hecketriangle.graded_ring import QuasiMeromorphicModularFormsRing
            sage: from sage.modular.modform_hecketriangle.space import QuasiMeromorphicModularForms
            sage: x,y,z,d = var("x,y,z,d")
            sage: QuasiMeromorphicModularFormsRing(n=5).Delta().full_reduce().denominator()
            1 + O(q^5)
            sage: QuasiMeromorphicModularFormsRing(n=5)((y^3-z^5)/(x^5-y^2)+y-d).denominator()
            f_rho^5 - f_i^2
            sage: QuasiMeromorphicModularFormsRing(n=5)((y^3-z^5)/(x^5-y^2)+y-d).denominator().parent()
            QuasiModularFormsRing(n=5) over Integer Ring
            sage: QuasiMeromorphicModularForms(n=5, k=-2, ep=-1)(x/y).denominator()
            1 - 13/(40*d)*q - 351/(64000*d^2)*q^2 - 13819/(76800000*d^3)*q^3 - 1163669/(491520000000*d^4)*q^4 + O(q^5)
            sage: QuasiMeromorphicModularForms(n=5, k=-2, ep=-1)(x/y).denominator().parent()
            QuasiModularForms(n=5, k=10/3, ep=-1) over Integer Ring
            sage: (QuasiMeromorphicModularForms(n=infinity, k=-6, ep=-1)(y/(x*(x-y^2)))).denominator()
            -64*q - 512*q^2 - 768*q^3 + 4096*q^4 + O(q^5)
            sage: (QuasiMeromorphicModularForms(n=infinity, k=-6, ep=-1)(y/(x*(x-y^2)))).denominator().parent()
            QuasiModularForms(n=+Infinity, k=8, ep=1) over Integer Ring
        """

        res = self.parent().rat_field()(self._rat.denominator())
        # In general the denominator has a different weight than the original function...
        new_parent = self.parent().extend_type("holo", ring=True).reduce_type(["holo", "quasi"])
        return new_parent(res).reduce()

    def _add_(self,other):
        r"""
        Return the sum of ``self`` and ``other``.

        EXAMPLES::

            sage: from sage.modular.modform_hecketriangle.graded_ring import QuasiMeromorphicModularFormsRing
            sage: from sage.modular.modform_hecketriangle.space import QuasiMeromorphicModularForms
            sage: MR = QuasiMeromorphicModularFormsRing(n=7)
            sage: E2 = MR.E2().full_reduce()
            sage: E4 = MR.E4().full_reduce()
            sage: E6 = MR.E6().full_reduce()
            sage: Delta = MR.Delta().full_reduce()
            sage: J_inv = MR.J_inv().full_reduce()
            sage: ring_el = MR(1/x+1).full_reduce()

            sage: (Delta^2*E2 + E6*E4^2).parent()
            QuasiModularFormsRing(n=7) over Integer Ring
            sage: E4 + Delta
            f_rho^15*d - f_rho^8*f_i^2*d + f_rho^5
            sage: (E4 + QQ(1) + ring_el).parent()
            MeromorphicModularFormsRing(n=7) over Integer Ring
            sage: (E4^3 + 1.1*Delta).parent()
            ModularForms(n=7, k=12, ep=1) over Real Field with 53 bits of precision
            sage: (E4 + FractionField(PolynomialRing(CC,'d')).gen()).parent()
            ModularFormsRing(n=7) over Complex Field with 53 bits of precision

            sage: subspace = MR.reduce_type(["holo"], degree=(12,1)).subspace([Delta, E6^2])
            sage: gen0 = subspace.gen(0)
            sage: gen1 = subspace.gen(1)
            sage: subspace2 = MR.reduce_type(["holo"], degree=(12,1)).subspace([Delta, Delta + E6^2])
            sage: gen2 = subspace2.gen(0)
            sage: gen3 = subspace2.gen(1)

            sage: (gen0 + gen1).parent()
            Subspace of dimension 2 of ModularForms(n=7, k=12, ep=1) over Integer Ring
            sage: (gen0 + Delta*J_inv).parent()
            WeakModularForms(n=7, k=12, ep=1) over Integer Ring
            sage: gen0 + E2
            f_rho^15*d - f_rho^8*f_i^2*d + E2
            sage: (gen0 + E2).parent()
            QuasiModularFormsRing(n=7) over Integer Ring
            sage: gen2 + ring_el
            (f_rho^16*d - f_rho^9*f_i^2*d + f_rho + 1)/f_rho
            sage: (gen0 + int(1)).parent()
            ModularFormsRing(n=7) over Integer Ring

            sage: from sage.modular.modform_hecketriangle.space import QuasiCuspForms, ModularForms
            sage: MF = ModularForms(k=20, ep=1)
            sage: QCF = QuasiCuspForms(k=20, ep=1)
            sage: el1 = QCF((MF.Delta()*MF.E2()^4))
            sage: el1 = QCF.subspace([el1])(el1)
            sage: el2 = MF(MF.E4()^2*MF.E6()^2)
            sage: el2 = MF.subspace([el2])(el2)
            sage: el3 = el1 + el2    # long time
            sage: el3    # long time
            1 - 527*q - 201288*q^2 + 61120668*q^3 + 20946799216*q^4 + O(q^5)
            sage: el3.parent()    # long time
            Subspace of dimension 2 of QuasiModularForms(n=3, k=20, ep=1) over Integer Ring

            sage: MF = ModularForms(n=infinity)
            sage: MF.E4() + MF.f_rho()
            E4 + 1
            sage: (MF.E4() + MF.f_rho()).parent()
            ModularFormsRing(n=+Infinity) over Integer Ring
            sage: MF.E4() + MF.f_i()^2
            2 - 32*q + 736*q^2 - 896*q^3 + 6368*q^4 + O(q^5)
            sage: (MF.E4() + MF.f_i()^2).parent()
            ModularForms(n=+Infinity, k=4, ep=1) over Integer Ring

            sage: el = ModularForms(n=3).Delta() + MF.E4()*MF.E6()
            sage: el
            (E4*f_i^4 - 2*E4^2*f_i^2 + E4^3 + 4096*E4^2*f_i)/4096
            sage: el.parent()
            ModularFormsRing(n=+Infinity) over Integer Ring
        """

        return self.parent()(self._rat+other._rat)

    def _sub_(self,other):
        r"""
        Return the difference of ``self`` and ``other``.

        EXAMPLES::

            sage: from sage.modular.modform_hecketriangle.graded_ring import QuasiMeromorphicModularFormsRing
            sage: from sage.modular.modform_hecketriangle.space import QuasiMeromorphicModularForms, ModularForms
            sage: MR = QuasiMeromorphicModularFormsRing(n=7)
            sage: E2 = MR.E2().full_reduce()
            sage: E4 = MR.E4().full_reduce()
            sage: E6 = MR.E6().full_reduce()
            sage: Delta = MR.Delta().full_reduce()
            sage: J_inv = MR.J_inv().full_reduce()
            sage: ring_el = MR(1/x+1).full_reduce()

            sage: E6^2-E4^3
            -1/d*q - 17/(56*d^2)*q^2 - 88887/(2458624*d^3)*q^3 - 941331/(481890304*d^4)*q^4 + O(q^5)
            sage: (E6^2-E4^3).parent()
            ModularForms(n=7, k=12, ep=1) over Integer Ring
            sage: (E4 - int(1)).parent()
            ModularFormsRing(n=7) over Integer Ring
            sage: E4 - FractionField(PolynomialRing(CC,'d')).gen()
            f_rho^5 - d
            sage: ((E4+E6)-E6).parent()
            ModularFormsRing(n=7) over Integer Ring

            sage: subspace = MR.reduce_type(["holo"], degree=(12,1)).subspace([Delta, E6^2])
            sage: gen0 = subspace.gen(0)
            sage: gen1 = subspace.gen(1)
            sage: subspace2 = MR.reduce_type(["holo"], degree=(12,1)).subspace([Delta, Delta + E6^2])
            sage: gen2 = subspace2.gen(0)
            sage: gen3 = subspace2.gen(1)

            sage: (gen0 - gen2).parent()
            Subspace of dimension 2 of ModularForms(n=7, k=12, ep=1) over Integer Ring
            sage: (gen2 - ring_el).parent()
            MeromorphicModularFormsRing(n=7) over Integer Ring
            sage: (gen0 - 1.1).parent()
            ModularFormsRing(n=7) over Real Field with 53 bits of precision

            sage: MF = ModularForms(n=infinity)
            sage: MF.E4() - MF.f_i()^2
            64*q - 512*q^2 + 1792*q^3 - 4096*q^4 + O(q^5)
            sage: (MF.E4() - MF.f_i()^2).parent()
            ModularForms(n=+Infinity, k=4, ep=1) over Integer Ring

            sage: el = ModularForms(n=3).Delta() - MF.E4()
            sage: el
            (E4*f_i^4 - 2*E4^2*f_i^2 + E4^3 - 4096*E4)/4096
            sage: el.parent()
            ModularFormsRing(n=+Infinity) over Integer Ring
        """

        #reduce at the end? See example "sage: ((E4+E6)-E6).parent()"
        return self.parent()(self._rat-other._rat)

    def _neg_(self):
        r"""
        Return the negation of ``self``.

        EXAMPLES::

            sage: from sage.modular.modform_hecketriangle.graded_ring import QuasiMeromorphicModularFormsRing
            sage: MR = QuasiMeromorphicModularFormsRing(n=8)
            sage: Delta = MR.Delta().full_reduce()

            sage: -Delta
            -q - 41/(128*d)*q^2 - 10887/(262144*d^2)*q^3 - 131447/(50331648*d^3)*q^4 + O(q^5)
            sage: parent(-Delta)
            CuspForms(n=8, k=12, ep=1) over Integer Ring

        Negation should be exactly the same as multiplication by -1::

            sage: (-Delta) == (-1) * Delta
            True
            sage: parent(-Delta) is parent((-1) * Delta)
            True
        """
        return self.parent()(-self._rat)

    def _mul_(self,other):
        r"""
        Return the product of ``self`` and ``other``.

        Note that the parent might (probably will) change.

        If ``parent.has_reduce_hom() == True`` then
        the result is reduced to be an element of
        the corresponding forms space if possible.

        In particular this is the case if both ``self``
        and ``other`` are (homogeneous) elements of a
        forms space.

        EXAMPLES::

            sage: from sage.modular.modform_hecketriangle.graded_ring import QuasiMeromorphicModularFormsRing
            sage: from sage.modular.modform_hecketriangle.space import QuasiMeromorphicModularForms, ModularForms
            sage: MR = QuasiMeromorphicModularFormsRing(n=8)
            sage: E2 = MR.E2().full_reduce()
            sage: E4 = MR.E4().full_reduce()
            sage: E6 = MR.E6().full_reduce()
            sage: Delta = MR.Delta().full_reduce()
            sage: J_inv = MR.J_inv().full_reduce()
            sage: ring_el = MR(1/x+1).full_reduce()

            sage: (1*Delta).parent()
            CuspForms(n=8, k=12, ep=1) over Integer Ring
            sage: (1.1*Delta).parent()
            ModularForms(n=8, k=12, ep=1) over Real Field with 53 bits of precision
            sage: (E2*E4).parent()
            QuasiModularForms(n=8, k=6, ep=-1) over Integer Ring
            sage: E4^2
            1 + 15/(32*d)*q + 3255/(32768*d^2)*q^2 + 105445/(8388608*d^3)*q^3 + 36379615/(34359738368*d^4)*q^4 + O(q^5)
            sage: (E4^2).parent()
            ModularForms(n=8, k=8, ep=1) over Integer Ring
            sage: (1.1*E4).parent()
            ModularForms(n=8, k=4, ep=1) over Real Field with 53 bits of precision
            sage: (J_inv*ring_el).parent()
            MeromorphicModularFormsRing(n=8) over Integer Ring
            sage: (E4*FractionField(PolynomialRing(CC,'d')).gen()).parent()
            ModularForms(n=8, k=4, ep=1) over Complex Field with 53 bits of precision

            sage: subspace = MR.reduce_type(["holo"], degree=(12,1)).subspace([Delta, E6^2])
            sage: gen0 = subspace.gen(0)
            sage: gen1 = subspace.gen(1)
            sage: subspace2 = MR.reduce_type(["holo"], degree=(12,1)).subspace([Delta, Delta + E6^2])
            sage: gen2 = subspace2.gen(0)
            sage: gen3 = subspace2.gen(1)

            sage: (gen0 * gen1).parent()
            ModularForms(n=8, k=24, ep=1) over Integer Ring
            sage: (gen0 * Delta*J_inv).parent()
            WeakModularForms(n=8, k=24, ep=1) over Integer Ring
            sage: (gen0 * Delta*J_inv).reduced_parent()
            CuspForms(n=8, k=24, ep=1) over Integer Ring
            sage: (gen0 * E2).parent()
            QuasiModularForms(n=8, k=14, ep=-1) over Integer Ring
            sage: gen2 * ring_el
            f_rho^18*d + f_rho^17*d - f_rho^10*f_i^2*d - f_rho^9*f_i^2*d
            sage: (gen2 * ring_el).parent()
            MeromorphicModularFormsRing(n=8) over Integer Ring
            sage: (1.1*gen0).parent()
            ModularForms(n=8, k=12, ep=1) over Real Field with 53 bits of precision

            sage: MF = ModularForms(n=infinity)
            sage: MF.E4()*MF.f_inf()
            q + 8*q^2 + 12*q^3 - 64*q^4 + O(q^5)
            sage: (MF.E4()*MF.f_inf()).parent()
            ModularForms(n=+Infinity, k=8, ep=1) over Integer Ring

            sage: el = ModularForms(n=3).E2()*MF.E6()
            sage: el
            1 - 8*q - 272*q^2 - 1760*q^3 - 2560*q^4 + O(q^5)
            sage: el.parent()
            QuasiModularForms(n=+Infinity, k=8, ep=1) over Integer Ring
        """

        res = self.parent().rat_field()(self._rat*other._rat)
        new_parent = self.parent().extend_type(ring=True)
        # The product of two homogeneous elements is homogeneous
        return new_parent(res).reduce()

    def _div_(self,other):
        r"""
        Return the division of ``self`` by ``other``.

        Note that the parent might (probably will) change.

        If ``parent.has_reduce_hom() == True`` then
        the result is reduced to be an element of
        the corresponding forms space if possible.

        In particular this is the case if both ``self``
        and ``other`` are (homogeneous) elements of a
        forms space.

        EXAMPLES::

            sage: from sage.modular.modform_hecketriangle.graded_ring import QuasiMeromorphicModularFormsRing
            sage: from sage.modular.modform_hecketriangle.space import QuasiMeromorphicModularForms, ModularForms
            sage: MR = QuasiMeromorphicModularFormsRing(n=8)
            sage: E2 = MR.E2().full_reduce()
            sage: E4 = MR.E4().full_reduce()
            sage: E6 = MR.E6().full_reduce()
            sage: Delta = MR.Delta().full_reduce()
            sage: J_inv = MR.J_inv().full_reduce()
            sage: ring_el = MR(1/x+1).full_reduce()

            sage: (1/Delta).parent()
            MeromorphicModularForms(n=8, k=-12, ep=1) over Integer Ring
            sage: (1.1/Delta).parent()
            MeromorphicModularForms(n=8, k=-12, ep=1) over Real Field with 53 bits of precision
            sage: (Delta/Delta).parent()
            MeromorphicModularForms(n=8, k=0, ep=1) over Integer Ring
            sage: 1/E4
            1 - 15/(64*d)*q + 2145/(65536*d^2)*q^2 - 59545/(16777216*d^3)*q^3 + 22622585/(68719476736*d^4)*q^4 + O(q^5)
            sage: (ring_el/J_inv).parent()
            MeromorphicModularFormsRing(n=8) over Integer Ring
            sage: (FractionField(PolynomialRing(CC,'d')).gen()/E4).parent()
            MeromorphicModularForms(n=8, k=-4, ep=1) over Complex Field with 53 bits of precision

            sage: (E4^(-2)).parent()
            MeromorphicModularForms(n=8, k=-8, ep=1) over Integer Ring
            sage: ((E4.as_ring_element())^(-2)).parent() == (E4^(-2)).parent()
            True
            sage: (MR(x)^(-3)).parent()
            QuasiMeromorphicModularFormsRing(n=8) over Integer Ring

            sage: subspace = MR.reduce_type(["holo"], degree=(12,1)).subspace([Delta, E6^2])
            sage: gen0 = subspace.gen(0)
            sage: gen1 = subspace.gen(1)
            sage: subspace2 = MR.reduce_type(["holo"], degree=(12,1)).subspace([Delta, Delta + E6^2])
            sage: gen2 = subspace2.gen(0)
            sage: gen3 = subspace2.gen(1)

            sage: (gen0 / gen1).parent()
            MeromorphicModularForms(n=8, k=0, ep=1) over Integer Ring
            sage: (gen0 / Delta).parent()
            MeromorphicModularForms(n=8, k=0, ep=1) over Integer Ring
            sage: ring_el / gen2
            (f_rho + 1)/(f_rho^19*d - f_rho^11*f_i^2*d)
            sage: (ring_el / gen2).parent()
            MeromorphicModularFormsRing(n=8) over Integer Ring
            sage: (1.1/gen0).parent()
            MeromorphicModularForms(n=8, k=-12, ep=1) over Real Field with 53 bits of precision

            sage: MF = ModularForms(n=infinity)
            sage: MF.f_i()/MF.E4()
            1 - 40*q + 552*q^2 - 4896*q^3 + 33320*q^4 + O(q^5)
            sage: (MF.f_i()/MF.E4()).parent()
            MeromorphicModularForms(n=+Infinity, k=-2, ep=-1) over Integer Ring
            sage: MF.f_i()/(MF.E4() + MF.f_i()^2)
            1/2 - 4*q - 236*q^2 - 2128*q^3 + 49428*q^4 + O(q^5)
            sage: (MF.f_i()/(MF.E4() + MF.f_i()^2)).parent()
            MeromorphicModularForms(n=+Infinity, k=-2, ep=-1) over Integer Ring

            sage: el = ModularForms(n=3).E2()/MF.E2()
            sage: el
            1 + 8*q + 48*q^2 + 480*q^3 + 4448*q^4 + O(q^5)
            sage: el.parent()
            QuasiMeromorphicModularForms(n=+Infinity, k=0, ep=1) over Integer Ring
        """

        res = self.parent().rat_field()(self._rat/other._rat)
        new_parent = self.parent().extend_type("mero", ring=True)
        # The division of two homogeneous elements is homogeneous
        return new_parent(res).reduce()

    def sqrt(self):
        r"""
        Try to return the square root of ``self``.
        I.e. the element corresponding to ``sqrt(self.rat())``.

        Whether this works or not depends on whether
        ``sqrt(self.rat())`` works and coerces into
        ``self.parent().rat_field()``.

        Note that the parent might (probably will) change.

        If ``parent.has_reduce_hom() == True`` then
        the result is reduced to be an element of
        the corresponding forms space if possible.

        In particular this is the case if ``self``
        is a (homogeneous) element of a forms space.

        .. TODO::

            Make square root in the underlying rational field work.

        EXAMPLES::

            sage: from sage.modular.modform_hecketriangle.space import QuasiModularForms
            sage: E2=QuasiModularForms(k=2, ep=-1).E2()
            sage: sqrt(E2^2)
            Traceback (most recent call last):
            ...
            NotImplementedError: is_square() not implemented for elements of Multivariate Polynomial Ring in x, y, z, d over Integer Ring
        """

        res = self.parent().rat_field()(self._rat.sqrt())
        new_parent = self.parent().extend_type(ring=True)
        # The sqrt of a homogeneous element is homogeneous if it exists
        return self.parent()(res).reduce()

    def diff_op(self, op, new_parent=None):
        r"""
        Return the differential operator ``op`` applied to ``self``.
        If ``parent.has_reduce_hom() == True`` then the result
        is reduced to be an element of the corresponding forms
        space if possible.

        INPUT:

        - ``op``          -- An element of ``self.parent().diff_alg()``.
                             I.e. an element of the algebra over ``QQ``
                             of differential operators generated
                             by ``X, Y, Z, dX, dY, DZ``, where e.g. ``X``
                             corresponds to the multiplication by ``x``
                             (resp. ``f_rho``) and ``dX`` corresponds to ``d/dx``.

                             To expect a homogeneous result after applying
                             the operator to a homogeneous element it should
                             should be homogeneous operator (with respect
                             to the usual, special grading).

        - ``new_parent``  -- Try to convert the result to the specified
                             ``new_parent``. If ``new_parent == None`` (default)
                             then the parent is extended to a
                             "quasi meromorphic" ring.

        OUTPUT:

        The new element.

        EXAMPLES::

            sage: from sage.modular.modform_hecketriangle.graded_ring import QuasiMeromorphicModularFormsRing
            sage: MR = QuasiMeromorphicModularFormsRing(n=8, red_hom=True)
            sage: (X,Y,Z,dX,dY,dZ) = MR.diff_alg().gens()
            sage: n=MR.hecke_n()
            sage: mul_op = 4/(n-2)*X*dX + 2*n/(n-2)*Y*dY + 2*Z*dZ
            sage: der_op = MR._derivative_op()
            sage: ser_op = MR._serre_derivative_op()
            sage: der_op == ser_op + (n-2)/(4*n)*Z*mul_op
            True

            sage: Delta = MR.Delta().full_reduce()
            sage: E2 = MR.E2().full_reduce()
            sage: Delta.diff_op(mul_op) == 12*Delta
            True
            sage: Delta.diff_op(mul_op).parent()
            QuasiMeromorphicModularForms(n=8, k=12, ep=1) over Integer Ring
            sage: Delta.diff_op(mul_op, Delta.parent()).parent()
            CuspForms(n=8, k=12, ep=1) over Integer Ring
            sage: E2.diff_op(mul_op, E2.parent()) == 2*E2
            True
            sage: Delta.diff_op(Z*mul_op, Delta.parent().extend_type("quasi", ring=True)) == 12*E2*Delta
            True

            sage: ran_op = X + Y*X*dY*dX + dZ + dX^2
            sage: Delta.diff_op(ran_op)
            f_rho^19*d + 306*f_rho^16*d - f_rho^11*f_i^2*d - 20*f_rho^10*f_i^2*d - 90*f_rho^8*f_i^2*d
            sage: E2.diff_op(ran_op)
            f_rho*E2 + 1

            sage: MR = QuasiMeromorphicModularFormsRing(n=infinity, red_hom=True)
            sage: (X,Y,Z,dX,dY,dZ) = MR.diff_alg().gens()
            sage: mul_op = 4*X*dX + 2*Y*dY + 2*Z*dZ
            sage: der_op = MR._derivative_op()
            sage: ser_op = MR._serre_derivative_op()
            sage: der_op == ser_op + Z/4*mul_op
            True

            sage: Delta = MR.Delta().full_reduce()
            sage: E2 = MR.E2().full_reduce()
            sage: Delta.diff_op(mul_op) == 12*Delta
            True
            sage: Delta.diff_op(mul_op).parent()
            QuasiMeromorphicModularForms(n=+Infinity, k=12, ep=1) over Integer Ring
            sage: Delta.diff_op(mul_op, Delta.parent()).parent()
            CuspForms(n=+Infinity, k=12, ep=1) over Integer Ring
            sage: E2.diff_op(mul_op, E2.parent()) == 2*E2
            True
            sage: Delta.diff_op(Z*mul_op, Delta.parent().extend_type("quasi", ring=True)) == 12*E2*Delta
            True

            sage: ran_op = X + Y*X*dY*dX + dZ + dX^2
            sage: Delta.diff_op(ran_op)
            -E4^3*f_i^2*d + E4^4*d - 4*E4^2*f_i^2*d - 2*f_i^2*d + 6*E4*d
            sage: E2.diff_op(ran_op)
            E4*E2 + 1
        """

        (x,y,z,d) = self.parent().rat_field().gens()
        (X,Y,Z,dX,dY,dZ) = self.parent().diff_alg().gens()
        L = op.monomials()
        new_rat = 0
        for mon in L:
            mon_summand  = self._rat
            mon_summand  = mon_summand.derivative(x,mon.degree(dX))
            mon_summand  = mon_summand.derivative(y,mon.degree(dY))
            mon_summand  = mon_summand.derivative(z,mon.degree(dZ))
            mon_summand *= x**(mon.degree(X))
            mon_summand *= y**(mon.degree(Y))
            mon_summand *= z**(mon.degree(Z))
            new_rat     += op.monomial_coefficient(mon)*mon_summand
        res = self.parent().rat_field()(new_rat)
        if (new_parent == None):
            new_parent = self.parent().extend_type(["quasi", "mero"], ring=True)
        return new_parent(res).reduce()

    # note that this is qd/dq, resp 1/(2*pi*i)*d/dtau
    def derivative(self):
        r"""
        Return the derivative ``d/dq = lambda/(2*pi*i) d/dtau`` of ``self``.

        Note that the parent might (probably will) change.
        In particular its analytic type will be extended
        to contain "quasi".

        If ``parent.has_reduce_hom() == True`` then
        the result is reduced to be an element of
        the corresponding forms space if possible.

        In particular this is the case if ``self``
        is a (homogeneous) element of a forms space.

        EXAMPLES::

            sage: from sage.modular.modform_hecketriangle.graded_ring import QuasiMeromorphicModularFormsRing
            sage: MR = QuasiMeromorphicModularFormsRing(n=7, red_hom=True)
            sage: n = MR.hecke_n()
            sage: E2 = MR.E2().full_reduce()
            sage: E6 = MR.E6().full_reduce()
            sage: f_rho = MR.f_rho().full_reduce()
            sage: f_i = MR.f_i().full_reduce()
            sage: f_inf = MR.f_inf().full_reduce()

            sage: derivative(f_rho) == 1/n * (f_rho*E2 - f_i)
            True
            sage: derivative(f_i)   == 1/2 * (f_i*E2 - f_rho**(n-1))
            True
            sage: derivative(f_inf) == f_inf * E2
            True
            sage: derivative(f_inf).parent()
            QuasiCuspForms(n=7, k=38/5, ep=-1) over Integer Ring
            sage: derivative(E2)    == (n-2)/(4*n) * (E2**2 - f_rho**(n-2))
            True
            sage: derivative(E2).parent()
            QuasiModularForms(n=7, k=4, ep=1) over Integer Ring

            sage: MR = QuasiMeromorphicModularFormsRing(n=infinity, red_hom=True)
            sage: E2 = MR.E2().full_reduce()
            sage: E4 = MR.E4().full_reduce()
            sage: E6 = MR.E6().full_reduce()
            sage: f_i = MR.f_i().full_reduce()
            sage: f_inf = MR.f_inf().full_reduce()

            sage: derivative(E4)    == E4 * (E2 - f_i)
            True
            sage: derivative(f_i)   == 1/2 * (f_i*E2 - E4)
            True
            sage: derivative(f_inf) == f_inf * E2
            True
            sage: derivative(f_inf).parent()
            QuasiModularForms(n=+Infinity, k=6, ep=-1) over Integer Ring
            sage: derivative(E2)    == 1/4 * (E2**2 - E4)
            True
            sage: derivative(E2).parent()
            QuasiModularForms(n=+Infinity, k=4, ep=1) over Integer Ring
        """

        return self.diff_op(self.parent()._derivative_op(), self.parent().extend_type("quasi", ring=True))

    def serre_derivative(self):
        r"""
        Return the Serre derivative of ``self``.

        Note that the parent might (probably will) change.
        However a modular element is returned if ``self``
        was already modular.

        If ``parent.has_reduce_hom() == True`` then
        the result is reduced to be an element of
        the corresponding forms space if possible.

        In particular this is the case if ``self``
        is a (homogeneous) element of a forms space.

        EXAMPLES::

            sage: from sage.modular.modform_hecketriangle.graded_ring import QuasiMeromorphicModularFormsRing
            sage: MR = QuasiMeromorphicModularFormsRing(n=7, red_hom=True)
            sage: n = MR.hecke_n()
            sage: Delta = MR.Delta().full_reduce()
            sage: E2 = MR.E2().full_reduce()
            sage: E4 = MR.E4().full_reduce()
            sage: E6 = MR.E6().full_reduce()
            sage: f_rho = MR.f_rho().full_reduce()
            sage: f_i = MR.f_i().full_reduce()
            sage: f_inf = MR.f_inf().full_reduce()

            sage: f_rho.serre_derivative() == -1/n * f_i
            True
            sage: f_i.serre_derivative()   == -1/2 * E4 * f_rho
            True
            sage: f_inf.serre_derivative() == 0
            True
            sage: E2.serre_derivative()    == -(n-2)/(4*n) * (E2^2 + E4)
            True
            sage: E4.serre_derivative()    == -(n-2)/n * E6
            True
            sage: E6.serre_derivative()    == -1/2 * E4^2 - (n-3)/n * E6^2 / E4
            True
            sage: E6.serre_derivative().parent()
            ModularForms(n=7, k=8, ep=1) over Integer Ring

            sage: MR = QuasiMeromorphicModularFormsRing(n=infinity, red_hom=True)
            sage: Delta = MR.Delta().full_reduce()
            sage: E2 = MR.E2().full_reduce()
            sage: E4 = MR.E4().full_reduce()
            sage: E6 = MR.E6().full_reduce()
            sage: f_i = MR.f_i().full_reduce()
            sage: f_inf = MR.f_inf().full_reduce()

            sage: E4.serre_derivative()    == -E4 * f_i
            True
            sage: f_i.serre_derivative()   == -1/2 * E4
            True
            sage: f_inf.serre_derivative() == 0
            True
            sage: E2.serre_derivative()    == -1/4 * (E2^2 + E4)
            True
            sage: E4.serre_derivative()    == -E6
            True
            sage: E6.serre_derivative()    == -1/2 * E4^2 - E6^2 / E4
            True
            sage: E6.serre_derivative().parent()
            ModularForms(n=+Infinity, k=8, ep=1) over Integer Ring
        """

        return self.diff_op(self.parent()._serre_derivative_op(), self.parent().extend_type(ring=True))

    @cached_method
    def order_at(self, tau=infinity):
        r"""
        Return the (overall) order of ``self`` at ``tau`` if easily possible:
        Namely if ``tau`` is ``infinity`` or congruent to ``i`` resp. ``rho``.

        It is possible to determine the order of points from ``HyperbolicPlane()``.
        In this case the coordinates of the upper half plane model are used.

        If ``self`` is homogeneous and modular then the rational function
        ``self.rat()`` is used. Otherwise only ``tau=infinity`` is supported
        by using the Fourier expansion with increasing precision
        (until the order can be determined).

        The function is mainly used to be able to work with the correct
        precision for Laurent series.

        .. NOTE::

            For quasi forms one cannot deduce the analytic type from
            this order at ``infinity`` since the analytic order is defined by the
            behavior on each quasi part and not by their linear combination.

        EXAMPLES::

            sage: from sage.modular.modform_hecketriangle.graded_ring import QuasiMeromorphicModularFormsRing
            sage: MR = QuasiMeromorphicModularFormsRing(red_hom=True)
            sage: (MR.Delta()^3).order_at(infinity)
            3
            sage: MR.E2().order_at(infinity)
            0
            sage: (MR.J_inv()^2).order_at(infinity)
            -2
            sage: x,y,z,d = MR.pol_ring().gens()
            sage: el = MR((z^3-y)^2/(x^3-y^2)).full_reduce()
            sage: el
            108*q + 11664*q^2 + 502848*q^3 + 12010464*q^4 + O(q^5)
            sage: el.order_at(infinity)
            1
            sage: el.parent()
            QuasiWeakModularForms(n=3, k=0, ep=1) over Integer Ring
            sage: el.is_holomorphic()
            False
            sage: MR((z-y)^2+(x-y)^3).order_at(infinity)
            2
            sage: MR((x-y)^10).order_at(infinity)
            10
            sage: MR.zero().order_at(infinity)
            +Infinity
            sage: (MR(x*y^2)/MR.J_inv()).order_at(i)
            2
            sage: (MR(x*y^2)/MR.J_inv()).order_at(MR.group().rho())
            -2

            sage: MR = QuasiMeromorphicModularFormsRing(n=infinity, red_hom=True)
            sage: (MR.Delta()^3*MR.E4()).order_at(infinity)
            3
            sage: MR.E2().order_at(infinity)
            0
            sage: (MR.J_inv()^2/MR.E4()).order_at(infinity)
            -2
            sage: el = MR((z^3-x*y)^2/(x^2*(x-y^2))).full_reduce()
            sage: el
            4*q - 304*q^2 + 8128*q^3 - 106144*q^4 + O(q^5)
            sage: el.order_at(infinity)
            1
            sage: el.parent()
            QuasiWeakModularForms(n=+Infinity, k=0, ep=1) over Integer Ring
            sage: el.is_holomorphic()
            False
            sage: MR((z-x)^2+(x-y)^3).order_at(infinity)
            2
            sage: MR((x-y)^10).order_at(infinity)
            10
            sage: MR.zero().order_at(infinity)
            +Infinity

            sage: (MR.j_inv()*MR.f_i()^3).order_at(-1)
            1
            sage: (MR.j_inv()*MR.f_i()^3).order_at(i)
            3
            sage: (1/MR.f_inf()^2).order_at(-1)
            0

            sage: p = HyperbolicPlane().PD().get_point(I)
            sage: MR((x-y)^10).order_at(p)
            10
            sage: MR.zero().order_at(p)
            +Infinity
        """

        i = QuadraticField(-1, 'I').gen()

        # if tau is a point of HyperbolicPlane then we use it's coordinates in the UHP model
        if (tau in HyperbolicPlane()):
            tau = tau.to_model('UHP').coordinates()

        if self.is_zero():
            return infinity

        if (self.is_homogeneous() and self.is_modular()):
            rat       = self.parent().rat_field()(self._rat)
            R         = self.parent().pol_ring()
            numerator = R(rat.numerator())
            denom     = R(rat.denominator())
            (x,y,z,d) = R.gens()
            n         = self.hecke_n()

            if (tau == i):
                f_pol = y
            # This includes the case rho=1 resp. n=infinity
            elif (tau == self.group().rho() or tau == -self.group().rho().conjugate()):
                f_pol = x
            # We intentionally leave out the d-factor!
            elif (tau == infinity):
                if (n == infinity):
                    f_pol = x - y**2
                else:
                    f_pol = x**n - y**2
            elif (tau.imag() > 0):
                if (self.group().in_FD(tau)):
                    raise NotImplementedError("Orders at general points (here: tau={}) are not yet implemented!".format(tau))
                else:
                    w = self.group().get_FD(tau)[1]
                    return self.order_at(w)
            else:
                raise ValueError("tau={} does not lie in the extended upper half plane!").format(tau)

            order_f = 0
            # There seems to be a bug in Singular, for now this "try, except" is a workaround
            # Also numerator /= f_pol doesn't seem to return an element of R for non-exact rings...
            try:
                while (f_pol.divides(numerator)):
                    numerator  = numerator.quo_rem(f_pol)[0]
                    #numerator /= f_pol
                    numerator  = R(numerator)
                    order_f += 1
            except TypeError:
                pass
            try:
                while (f_pol.divides(denom)):
                    denom      = denom.quo_rem(f_pol)[0]
                    #denom     /= f_pol
                    denom      = R(denom)
                    order_f -= 1
            except TypeError:
                pass

            return order_f
        else:
            if (tau != infinity):
                raise NotImplementedError("Only the order at infinity is supported for non-homogeneous or quasi forms!")

            num_val   = prec_num_bound   = 1 #(self.parent()._prec/ZZ(2)).ceil()
            denom_val = prec_denom_bound = 1 #(self.parent()._prec/ZZ(2)).ceil()

            while (num_val >= prec_num_bound):
                prec_num_bound   *= 2
                num_val   = self.numerator().q_expansion(prec=prec_num_bound, fix_prec=True).valuation()
            while (denom_val >= prec_denom_bound):
                prec_denom_bound *= 2
                denom_val = self.denominator().q_expansion(prec=prec_denom_bound, fix_prec=True).valuation()

            return (num_val-denom_val)

    def as_ring_element(self):
        r"""
        Coerce ``self`` into the graded ring of its parent.

        EXAMPLES::

            sage: from sage.modular.modform_hecketriangle.space import CuspForms
            sage: Delta = CuspForms(k=12).Delta()
            sage: Delta.parent()
            CuspForms(n=3, k=12, ep=1) over Integer Ring
            sage: Delta.as_ring_element()
            f_rho^3*d - f_i^2*d
            sage: Delta.as_ring_element().parent()
            CuspFormsRing(n=3) over Integer Ring

            sage: CuspForms(n=infinity, k=12).Delta().as_ring_element()
            -E4^2*f_i^2*d + E4^3*d
        """

        return self.parent().graded_ring()(self._rat)

    def reduce(self, force=False):
        r"""
        In case ``self.parent().has_reduce_hom() == True``
        (or ``force==True``) and ``self`` is homogeneous
        the converted element lying in the corresponding
        homogeneous_part is returned.

        Otherwise ``self`` is returned.

        EXAMPLES::

            sage: from sage.modular.modform_hecketriangle.graded_ring import ModularFormsRing
            sage: E2 = ModularFormsRing(n=7).E2().reduce()
            sage: E2.parent()
            QuasiModularFormsRing(n=7) over Integer Ring
            sage: E2 = ModularFormsRing(n=7, red_hom=True).E2().reduce()
            sage: E2.parent()
            QuasiModularForms(n=7, k=2, ep=-1) over Integer Ring
            sage: ModularFormsRing(n=7)(x+1).reduce().parent()
            ModularFormsRing(n=7) over Integer Ring
            sage: E2 = ModularFormsRing(n=7).E2().reduce(force=True)
            sage: E2.parent()
            QuasiModularForms(n=7, k=2, ep=-1) over Integer Ring
            sage: ModularFormsRing(n=7)(x+1).reduce(force=True).parent()
            ModularFormsRing(n=7) over Integer Ring

            sage: y=var("y")
            sage: ModularFormsRing(n=infinity)(x-y^2).reduce(force=True)
            64*q - 512*q^2 + 1792*q^3 - 4096*q^4 + O(q^5)
        """

        if (force or self.parent().has_reduce_hom()) and self.is_homogeneous():
            return self.parent().homogeneous_part(self._weight, self._ep)(self._rat)
        else:
            return self

    def reduced_parent(self):
        r"""
        Return the space with the analytic type of ``self``.
        If ``self`` is homogeneous the corresponding ``FormsSpace`` is returned.

        I.e. return the smallest known ambient space of ``self``.

        EXAMPLES::

            sage: from sage.modular.modform_hecketriangle.graded_ring import QuasiMeromorphicModularFormsRing
            sage: Delta = QuasiMeromorphicModularFormsRing(n=7).Delta()
            sage: Delta.parent()
            QuasiMeromorphicModularFormsRing(n=7) over Integer Ring
            sage: Delta.reduced_parent()
            CuspForms(n=7, k=12, ep=1) over Integer Ring
            sage: el = QuasiMeromorphicModularFormsRing()(x+1)
            sage: el.parent()
            QuasiMeromorphicModularFormsRing(n=3) over Integer Ring
            sage: el.reduced_parent()
            ModularFormsRing(n=3) over Integer Ring

            sage: y=var("y")
            sage: QuasiMeromorphicModularFormsRing(n=infinity)(x-y^2).reduced_parent()
            ModularForms(n=+Infinity, k=4, ep=1) over Integer Ring
            sage: QuasiMeromorphicModularFormsRing(n=infinity)(x*(x-y^2)).reduced_parent()
            CuspForms(n=+Infinity, k=8, ep=1) over Integer Ring
        """

        if self.is_homogeneous():
            return FormsSpace(self.analytic_type(), self.group(), self.base_ring(), self.weight(), self.ep())
        else:
            return FormsRing(self.analytic_type(), self.group(), self.base_ring(), self.parent().has_reduce_hom())

    def full_reduce(self):
        r"""
        Convert ``self`` into its reduced parent.

        EXAMPLES::

            sage: from sage.modular.modform_hecketriangle.graded_ring import QuasiMeromorphicModularFormsRing
            sage: Delta = QuasiMeromorphicModularFormsRing().Delta()
            sage: Delta
            f_rho^3*d - f_i^2*d
            sage: Delta.full_reduce()
            q - 24*q^2 + 252*q^3 - 1472*q^4 + O(q^5)
            sage: Delta.full_reduce().parent() == Delta.reduced_parent()
            True

            sage: QuasiMeromorphicModularFormsRing().Delta().full_reduce().parent()
            CuspForms(n=3, k=12, ep=1) over Integer Ring
        """

        return self.reduced_parent()(self._rat)

    #precision is actually acuracy, maybe add "real precision" meaning number of rel. coef
    @cached_method
    def _q_expansion_cached(self, prec, fix_d, subs_d, d_num_prec, fix_prec = False):
        """
        Returns the Fourier expansion of self (cached).
        Don't call this function, instead use :meth:`q_expansion`.
        Also see :meth:`q_expansion` for a description of the arguments.

        Regarding the additional option ``subs_d``:
        Caching doesn't distinguish between ``True`` and ``1``. If ``fix_d`` is
        not boolean then ``subs_d=fix_d`` should be set make that distinction.

        EXAMPLES::

            sage: from sage.modular.modform_hecketriangle.graded_ring import WeakModularFormsRing
            sage: J_inv = WeakModularFormsRing(red_hom=True).J_inv()
            sage: J_inv._q_expansion_cached(prec=5, fix_d=False, subs_d=None, d_num_prec=53, fix_prec=False) == J_inv.q_expansion()
            True
            sage: J_inv._q_expansion_cached(prec=5, fix_d=True, subs_d=None, d_num_prec=53, fix_prec=False) == J_inv.q_expansion_fixed_d()
            True
        """

        if (fix_prec == False):
            #if (prec <1):
            #    print "Warning: non-positive precision!"
            if ((not self.is_zero()) and prec <= self.order_at(infinity)):
                from warnings import warn
                warn("precision too low to determine any coefficient!")

            # This should _exactly_ ensure the given precision O(q^prec):
            prec += self.denominator().order_at(infinity) + max(-self.order_at(infinity), 0)

            # The result will have "max(prec-self.order_at(infinity),0)" significant coefficients
            # So adding the following line to the above one
            # would instead give "prec" many significant coefficients:
            # prec += self.order_at(infinity)

        SC = MFSeriesConstructor(self.group(), prec)
        formal_d = self.parent().get_d()
        formal_q = self.parent().get_q(prec)

        if (self.hecke_n() == infinity):
            X = SC.E4_ZZ().base_extend(formal_d.parent())
        else:
            X = SC.f_rho_ZZ().base_extend(formal_d.parent())
        Y  = SC.f_i_ZZ().base_extend(formal_d.parent())

        if (self.parent().is_modular()):
            qexp = self._rat.subs(x=X, y=Y, d=formal_d)
        else:
            Z = SC.E2_ZZ().base_extend(formal_d.parent())
            qexp = self._rat.subs(x=X, y=Y, z=Z, d=formal_d)

        qexp = (qexp + O(formal_q**prec)).parent()(qexp)
        qexp = qexp(formal_q/formal_d)
        cur_prec = qexp.prec()

        if (subs_d):
            fix_d = subs_d
        d = self.parent().get_d(fix_d, d_num_prec)
        q = self.parent().get_q(prec, fix_d, d_num_prec)

        qexp = sum([(qexp.coefficients()[m]).subs(d=d) * q**qexp.exponents()[m] for m in range(len(qexp.coefficients()))])
        if (cur_prec != infinity):
            qexp += O(q**cur_prec)
        else:
            qexp = (qexp + O(q)).parent()(qexp)

        return qexp

    def q_expansion(self, prec = None, fix_d = False, d_num_prec = None, fix_prec = False):
        """
        Returns the Fourier expansion of self.

        INPUT:

        - ``prec``       -- An integer, the desired output precision O(q^prec).
                            Default: ``None`` in which case the default precision
                            of ``self.parent()`` is used.

        - ``fix_d``      -- If ``False`` (default) a formal parameter is used for ``d``.
                            If ``True`` then the numerical value of ``d`` is used
                            (resp. an exact value if the group is arithmetic).
                            Otherwise the given value is used for ``d``.

        - ``d_num_prec`` -- The precision to be used if a numerical value for ``d`` is substituted.
                            Default: ``None`` in which case the default
                            numerical precision of ``self.parent()`` is used.

        - ``fix_prec``   -- If ``fix_prec`` is not ``False`` (default)
                            then the precision of the ``MFSeriesConstructor`` is
                            increased such that the output has exactly the specified
                            precision O(q^prec).

        OUTPUT:

        The Fourier expansion of self as a ``FormalPowerSeries`` or ``FormalLaurentSeries``.

        EXAMPLES::

            sage: from sage.modular.modform_hecketriangle.graded_ring import WeakModularFormsRing, QuasiModularFormsRing
            sage: j_inv = WeakModularFormsRing(red_hom=True).j_inv()
            sage: j_inv.q_expansion(prec=3)
            q^-1 + 31/(72*d) + 1823/(27648*d^2)*q + 10495/(2519424*d^3)*q^2 + O(q^3)

            sage: E2 = QuasiModularFormsRing(n=5, red_hom=True).E2()
            sage: E2.q_expansion(prec=3)
            1 - 9/(200*d)*q - 369/(320000*d^2)*q^2 + O(q^3)
            sage: E2.q_expansion(prec=3, fix_d=1)
            1 - 9/200*q - 369/320000*q^2 + O(q^3)

            sage: E6 = WeakModularFormsRing(n=5, red_hom=True).E6().full_reduce()
            sage: Delta = WeakModularFormsRing(n=5, red_hom=True).Delta().full_reduce()
            sage: E6.q_expansion(prec=3).prec() == 3
            True
            sage: (Delta/(E2^3-E6)).q_expansion(prec=3).prec() == 3
            True
            sage: (Delta/(E2^3-E6)^3).q_expansion(prec=3).prec() == 3
            True
            sage: ((E2^3-E6)/Delta^2).q_expansion(prec=3).prec() == 3
            True
            sage: ((E2^3-E6)^3/Delta).q_expansion(prec=3).prec() == 3
            True

            sage: x,y = var("x,y")
            sage: el = WeakModularFormsRing()((x+1)/(x^3-y^2))
            sage: el.q_expansion(prec=2, fix_prec = True)
            2*d*q^-1 + O(1)
            sage: el.q_expansion(prec=2)
            2*d*q^-1 + 1/6 + 119/(41472*d)*q + O(q^2)

            sage: j_inv = WeakModularFormsRing(n=infinity, red_hom=True).j_inv()
            sage: j_inv.q_expansion(prec=3)
            q^-1 + 3/(8*d) + 69/(1024*d^2)*q + 1/(128*d^3)*q^2 + O(q^3)

            sage: E2 = QuasiModularFormsRing(n=infinity, red_hom=True).E2()
            sage: E2.q_expansion(prec=3)
            1 - 1/(8*d)*q - 1/(512*d^2)*q^2 + O(q^3)
            sage: E2.q_expansion(prec=3, fix_d=1)
            1 - 1/8*q - 1/512*q^2 + O(q^3)

            sage: E4 = WeakModularFormsRing(n=infinity, red_hom=True).E4().full_reduce()
            sage: Delta = WeakModularFormsRing(n=infinity, red_hom=True).Delta().full_reduce()
            sage: E4.q_expansion(prec=3).prec() == 3
            True
            sage: (Delta/(E2^2-E4)).q_expansion(prec=3).prec() == 3
            True
            sage: (Delta/(E2^2-E4)^3).q_expansion(prec=3).prec() == 3
            True
            sage: ((E2^2-E4)/Delta^2).q_expansion(prec=3).prec() == 3
            True
            sage: ((E2^2-E4)^3/Delta).q_expansion(prec=3).prec() == 3
            True

            sage: x,y = var("x,y")
            sage: el = WeakModularFormsRing(n=infinity)((x+1)/(x-y^2))
            sage: el.q_expansion(prec=2, fix_prec = True)
            2*d*q^-1 + O(1)
            sage: el.q_expansion(prec=2)
            2*d*q^-1 + 1/2 + 39/(512*d)*q + O(q^2)
        """

        if prec == None:
            prec = self.parent().default_prec()
        if d_num_prec == None:
            d_num_prec = self.parent().default_num_prec()
        if not isinstance(fix_d, bool):
            subs_d = fix_d
            fix_d = None
        else:
            subs_d = None

        return self._q_expansion_cached(prec, fix_d, subs_d, d_num_prec, fix_prec)

    def q_expansion_fixed_d(self, prec = None, d_num_prec = None, fix_prec = False):
        """
        Returns the Fourier expansion of self.
        The numerical (or exact) value for ``d`` is substituted.


        INPUT:

        - ``prec``       -- An integer, the desired output precision O(q^prec).
                            Default: ``None`` in which case the default precision
                            of ``self.parent()`` is used.

        - ``d_num_prec`` -- The precision to be used if a numerical value for ``d`` is substituted.
                            Default: ``None`` in which case the default
                            numerical precision of ``self.parent()`` is used.

        - ``fix_prec``   -- If ``fix_prec`` is not ``False`` (default)
                            then the precision of the ``MFSeriesConstructor`` is
                            increased such that the output has exactly the specified
                            precision O(q^prec).

        OUTPUT:

        The Fourier expansion of self as a ``FormalPowerSeries`` or ``FormalLaurentSeries``.

        EXAMPLES::

            sage: from sage.modular.modform_hecketriangle.graded_ring import WeakModularFormsRing, QuasiModularFormsRing
            sage: j_inv = WeakModularFormsRing(red_hom=True).j_inv()
            sage: j_inv.q_expansion_fixed_d(prec=3)
            q^-1 + 744 + 196884*q + 21493760*q^2 + O(q^3)

            sage: E2 = QuasiModularFormsRing(n=5, red_hom=True).E2()
            sage: E2.q_expansion_fixed_d(prec=3)
            1.000000000000... - 6.380956565426...*q - 23.18584547617...*q^2 + O(q^3)

            sage: x,y = var("x,y")
            sage: WeakModularFormsRing()((x+1)/(x^3-y^2)).q_expansion_fixed_d(prec=2, fix_prec = True)
            1/864*q^-1 + O(1)
            sage: WeakModularFormsRing()((x+1)/(x^3-y^2)).q_expansion_fixed_d(prec=2)
            1/864*q^-1 + 1/6 + 119/24*q + O(q^2)

            sage: j_inv = WeakModularFormsRing(n=infinity, red_hom=True).j_inv()
            sage: j_inv.q_expansion_fixed_d(prec=3)
            q^-1 + 24 + 276*q + 2048*q^2 + O(q^3)

            sage: E2 = QuasiModularFormsRing(n=infinity, red_hom=True).E2()
            sage: E2.q_expansion_fixed_d(prec=3)
            1 - 8*q - 8*q^2 + O(q^3)

            sage: x,y = var("x,y")
            sage: WeakModularFormsRing(n=infinity)((x+1)/(x-y^2)).q_expansion_fixed_d(prec=2, fix_prec = True)
            1/32*q^-1 + O(1)
            sage: WeakModularFormsRing(n=infinity)((x+1)/(x-y^2)).q_expansion_fixed_d(prec=2)
            1/32*q^-1 + 1/2 + 39/8*q + O(q^2)

            sage: (WeakModularFormsRing(n=14).J_inv()^3).q_expansion_fixed_d(prec=2)
            2.933373093...e-6*q^-3 + 0.0002320999814...*q^-2 + 0.009013529265...*q^-1 + 0.2292916854... + 4.303583833...*q + O(q^2)
        """

        return self.q_expansion(prec, True, d_num_prec, fix_prec)

    def q_expansion_vector(self, min_exp = None, max_exp = None, prec = None, **kwargs):
        r"""
        Return (part of) the Laurent series expansion of ``self`` as a vector.

        INPUT:

        - ``min_exp`` -- An integer, specifying the first coefficient to be
                         used for the vector. Default: ``None``, meaning that
                         the first non-trivial coefficient is used.

        - ``max_exp``  -- An integer, specifying the last coefficient to be
                          used for the vector. Default: ``None``, meaning that
                          the default precision + 1 is used.

        - ``prec``     -- An integer, specifying the precision of the underlying
                          Laurent series. Default: ``None``, meaning that
                          ``max_exp + 1`` is used.

        OUTPUT:

        A vector of size ``max_exp - min_exp`` over the coefficient ring of self,
        determined by the corresponding Laurent series coefficients.

        EXAMPLES::

            sage: from sage.modular.modform_hecketriangle.graded_ring import WeakModularFormsRing
            sage: f = WeakModularFormsRing(red_hom=True).j_inv()^3
            sage: f.q_expansion(prec=3)
            q^-3 + 31/(24*d)*q^-2 + 20845/(27648*d^2)*q^-1 + 7058345/(26873856*d^3) + 30098784355/(495338913792*d^4)*q + 175372747465/(17832200896512*d^5)*q^2 + O(q^3)
            sage: v = f.q_expansion_vector(max_exp=1, prec=3)
            sage: v
            (1, 31/(24*d), 20845/(27648*d^2), 7058345/(26873856*d^3), 30098784355/(495338913792*d^4))
            sage: v.parent()
            Vector space of dimension 5 over Fraction Field of Univariate Polynomial Ring in d over Integer Ring
            sage: f.q_expansion_vector(min_exp=1, max_exp=2)
            (30098784355/(495338913792*d^4), 175372747465/(17832200896512*d^5))
            sage: f.q_expansion_vector(min_exp=1, max_exp=2, fix_d=True)
            (541778118390, 151522053809760)

            sage: f = WeakModularFormsRing(n=infinity, red_hom=True).j_inv()^3
            sage: f.q_expansion_fixed_d(prec=3)
            q^-3 + 72*q^-2 + 2556*q^-1 + 59712 + 1033974*q + 14175648*q^2 + O(q^3)
            sage: v = f.q_expansion_vector(max_exp=1, prec=3, fix_d=True)
            sage: v
            (1, 72, 2556, 59712, 1033974)
            sage: v.parent()
            Vector space of dimension 5 over Rational Field
            sage: f.q_expansion_vector(min_exp=1, max_exp=2)
            (516987/(8388608*d^4), 442989/(33554432*d^5))
        """

        if (max_exp == None):
            max_exp = self.parent().default_prec() - 1
        else:
            max_exp = ZZ(max_exp)
        if (prec == None):
            prec = max_exp + 1
        else:
            prec = ZZ(prec)
            if (prec < max_exp + 1):
                raise ValueError("The specified precision is too low: {} < {}".format(prec, max_exp + 1))

        qexp = self.q_expansion(prec=prec, **kwargs)

        if (min_exp == None):
            min_exp = qexp.valuation()
        else:
            min_exp = ZZ(min_exp)

        return vector([qexp[m] for m in range(min_exp, max_exp +1)])

    def evaluate(self, tau, prec = None, num_prec = None, check=False):
        r"""
        Try to return ``self`` evaluated at a point ``tau``
        in the upper half plane, where ``self`` is interpreted
        as a function in ``tau``, where ``q=exp(2*pi*i*tau)``.

        Note that this interpretation might not make sense
        (and fail) for certain (many) choices of
        (``base_ring``, ``tau.parent()``).

        It is possible to evalutate at points of ``HyperbolicPlane()``.
        In this case the coordinates of the upper half plane model are used.

        To obtain a precise and fast result the parameters
        ``prec`` and ``num_prec`` both have to be considered/balanced.
        A high ``prec`` value is usually quite costly.

        INPUT:

        - ``tau``       -- ``infinity`` or an element of the upper
                           half plane. E.g. with parent ``AA`` or ``CC``.

        - ``prec``      -- An integer, namely the precision used for the
                           Fourier expansion. If ``prec == None`` (default)
                           then the default precision of ``self.parent()``
                           is used.

        - ``num_prec``  -- An integer, namely the minimal numerical precision
                           used for ``tau`` and ``d``. If ``num_prec == None``
                           (default) then the default numerical precision of
                           ``self.parent()`` is used.

        - ``check``     -- If ``True`` then the order of ``tau`` is checked.
                           Otherwise the order is only considered for
                           ``tau = infinity, i, rho, -1/rho``. Default: ``False``.

        OUTPUT:

        The (numerical) evaluated function value.


        ALGORITHM:

        #. If the order of ``self`` at ``tau`` is known and nonzero:
           Return ``0`` resp. ``infinity``.

        #. Else if ``tau==infinity`` and the order is zero:
           Return the constant Fourier coefficient of ``self``.

        #. Else if ``self`` is homogeneous and modular:

           #. Because of the (modular) transformation property
              of ``self`` the evaluation at ``tau`` is given by
              the evaluation at ``w`` multiplied by ``aut_factor(A,w)``.

           #. The evaluation at ``w`` is calculated by
              evaluating the truncated Fourier expansion of
              self at ``q(w)``.

           Note that this is much faster and more precise
           than a direct evaluation at ``tau``.

        #. Else if ``self`` is exactly ``E2``:

           #. The same procedure as before is applied (with
              the aut_factor from the corresponding modular
              space).

           #. Except that at the end a correction term for
              the quasimodular form ``E2`` of the form
              ``4*lambda/(2*pi*i)*n/(n-2) * c*(c*w + d)``
              (resp. ``4/(pi*i) * c*(c*w + d)`` for ``n=infinity``)
              has to be added, where ``lambda = 2*cos(pi/n)``
              (resp ``lambda = 2`` for ``n=infinity``) and
              ``c,d`` are the lower entries of the matrix ``A``.

        #. Else:

           #. Evaluate ``f_rho, f_i, E2`` at ``tau``
              using the above procedures.
              If ``n=infinity`` use ``E4`` instead of ``f_rho``.

           #. Substitute ``x=f_rho(tau), y=f_i(tau), z=E2(tau)``
              and the numerical value of ``d`` for ``d``
              in ``self.rat()``. If ``n=infinity`` then
              subsitute ``x=E4(tau)`` instead.

        EXAMPLES::

            sage: from sage.modular.modform_hecketriangle.hecke_triangle_groups import HeckeTriangleGroup
            sage: from sage.modular.modform_hecketriangle.graded_ring import QuasiMeromorphicModularFormsRing
            sage: MR = QuasiMeromorphicModularFormsRing(n=5, red_hom=True)
            sage: f_rho = MR.f_rho().full_reduce()
            sage: f_i   = MR.f_i().full_reduce()
            sage: f_inf = MR.f_inf().full_reduce()
            sage: E2    = MR.E2().full_reduce()
            sage: E4    = MR.E4().full_reduce()
            sage: rho   = MR.group().rho()

            sage: f_rho(rho)
            0
            sage: f_rho(rho + 1e-100)    # since rho == rho + 1e-100
            0
            sage: f_rho(rho + 1e-6)
            2.525...e-10 - 3.884...e-6*I
            sage: f_i(i)
            0
            sage: f_i(i + 1e-1000)
            -6.084...e-14 - 4.101...e-1000*I
            sage: f_inf(infinity)
            0

            sage: i = I = QuadraticField(-1, 'I').gen()
            sage: z = -1/(-1/(2*i+30)-1)
            sage: z
            2/965*I + 934/965
            sage: E4(z)
            32288.05588811... - 118329.8566016...*I
            sage: E4(z, prec=30, num_prec=100)    # long time
            32288.0558872351130041311053... - 118329.856600349999751420381...*I
            sage: E2(z)
            409.3144737105... + 100.6926857489...*I
            sage: E2(z, prec=30, num_prec=100)    # long time
            409.314473710489761254584951... + 100.692685748952440684513866...*I
            sage: (E2^2-E4)(z)
            125111.2655383... + 200759.8039479...*I
            sage: (E2^2-E4)(z, prec=30, num_prec=100)    # long time
            125111.265538336196262200469... + 200759.803948009905410385699...*I

            sage: (E2^2-E4)(infinity)
            0
            sage: (1/(E2^2-E4))(infinity)
            +Infinity
            sage: ((E2^2-E4)/f_inf)(infinity)
            -3/(10*d)

            sage: G = HeckeTriangleGroup(n=8)
            sage: MR = QuasiMeromorphicModularFormsRing(group=G, red_hom=True)
            sage: f_rho = MR.f_rho().full_reduce()
            sage: f_i   = MR.f_i().full_reduce()
            sage: E2    = MR.E2().full_reduce()

            sage: z = AlgebraicField()(1/10+13/10*I)
            sage: A = G.V(4)
            sage: S = G.S()
            sage: T = G.T()
            sage: A == (T*S)**3*T
            True
            sage: az = A.acton(z)
            sage: az == (A[0,0]*z + A[0,1]) / (A[1,0]*z + A[1,1])
            True

            sage: f_rho(z)
            1.03740476727... + 0.0131941034523...*I
            sage: f_rho(az)
            -2.29216470688... - 1.46235057536...*I
            sage: k = f_rho.weight()
            sage: aut_fact = f_rho.ep()^3 * (((T*S)**2*T).acton(z)/AlgebraicField()(i))**k * (((T*S)*T).acton(z)/AlgebraicField()(i))**k * (T.acton(z)/AlgebraicField()(i))**k
            sage: abs(aut_fact - f_rho.parent().aut_factor(A, z)) < 1e-12
            True
            sage: aut_fact * f_rho(z)
            -2.29216470688... - 1.46235057536...*I

            sage: f_rho.parent().default_num_prec(1000)
            sage: f_rho.parent().default_prec(300)
            sage: (f_rho.q_expansion_fixed_d().polynomial())(exp((2*pi*i).n(1000)*z/G.lam()))    # long time
            1.0374047672719462149821251... + 0.013194103452368974597290332...*I
            sage: (f_rho.q_expansion_fixed_d().polynomial())(exp((2*pi*i).n(1000)*az/G.lam()))    # long time
            -2.2921647068881834598616367... - 1.4623505753697635207183406...*I

            sage: f_i(z)
            0.667489320423... - 0.118902824870...*I
            sage: f_i(az)
            14.5845388476... - 28.4604652892...*I
            sage: k = f_i.weight()
            sage: aut_fact = f_i.ep()^3 * (((T*S)**2*T).acton(z)/AlgebraicField()(i))**k * (((T*S)*T).acton(z)/AlgebraicField()(i))**k * (T.acton(z)/AlgebraicField()(i))**k
            sage: abs(aut_fact - f_i.parent().aut_factor(A, z)) < 1e-12
            True
            sage: aut_fact * f_i(z)
            14.5845388476... - 28.4604652892...*I

            sage: f_i.parent().default_num_prec(1000)
            sage: f_i.parent().default_prec(300)
            sage: (f_i.q_expansion_fixed_d().polynomial())(exp((2*pi*i).n(1000)*z/G.lam()))    # long time
            0.66748932042300250077433252... - 0.11890282487028677063054267...*I
            sage: (f_i.q_expansion_fixed_d().polynomial())(exp((2*pi*i).n(1000)*az/G.lam()))    # long time
            14.584538847698600875918891... - 28.460465289220303834894855...*I

            sage: f = f_rho*E2
            sage: f(z)
            0.966024386418... - 0.0138894699429...*I
            sage: f(az)
            -15.9978074989... - 29.2775758341...*I
            sage: k = f.weight()
            sage: aut_fact = f.ep()^3 * (((T*S)**2*T).acton(z)/AlgebraicField()(i))**k * (((T*S)*T).acton(z)/AlgebraicField()(i))**k * (T.acton(z)/AlgebraicField()(i))**k
            sage: abs(aut_fact - f.parent().aut_factor(A, z)) < 1e-12
            True
            sage: k2 = f_rho.weight()
            sage: aut_fact2 = f_rho.ep() * (((T*S)**2*T).acton(z)/AlgebraicField()(i))**k2 * (((T*S)*T).acton(z)/AlgebraicField()(i))**k2 * (T.acton(z)/AlgebraicField()(i))**k2
            sage: abs(aut_fact2 - f_rho.parent().aut_factor(A, z)) < 1e-12
            True
            sage: cor_term = (4 * G.n() / (G.n()-2) * A.c() * (A.c()*z+A.d())) / (2*pi*i).n(1000) * G.lam()
            sage: aut_fact*f(z) + cor_term*aut_fact2*f_rho(z)
            -15.9978074989... - 29.2775758341...*I

            sage: f.parent().default_num_prec(1000)
            sage: f.parent().default_prec(300)
            sage: (f.q_expansion_fixed_d().polynomial())(exp((2*pi*i).n(1000)*z/G.lam()))    # long time
            0.96602438641867296777809436... - 0.013889469942995530807311503...*I
            sage: (f.q_expansion_fixed_d().polynomial())(exp((2*pi*i).n(1000)*az/G.lam()))    # long time
            -15.997807498958825352887040... - 29.277575834123246063432206...*I

            sage: MR = QuasiMeromorphicModularFormsRing(n=infinity, red_hom=True)
            sage: f_i   = MR.f_i().full_reduce()
            sage: f_inf = MR.f_inf().full_reduce()
            sage: E2    = MR.E2().full_reduce()
            sage: E4    = MR.E4().full_reduce()

            sage: f_i(i)
            0
            sage: f_i(i + 1e-1000)
            2.991...e-12 - 3.048...e-1000*I
            sage: f_inf(infinity)
            0

            sage: z = -1/(-1/(2*i+30)-1)
            sage: E4(z, prec=15)
            804.0722034... + 211.9278206...*I
            sage: E4(z, prec=30, num_prec=100)    # long time
            803.928382417... + 211.889914044...*I
            sage: E2(z)
            2.438455612... - 39.48442265...*I
            sage: E2(z, prec=30, num_prec=100)    # long time
            2.43968197227756036957475... - 39.4842637577742677851431...*I
            sage: (E2^2-E4)(z)
            -2265.442515... - 380.3197877...*I
            sage: (E2^2-E4)(z, prec=30, num_prec=100)    # long time
            -2265.44251550679807447320... - 380.319787790548788238792...*I

            sage: (E2^2-E4)(infinity)
            0
            sage: (1/(E2^2-E4))(infinity)
            +Infinity
            sage: ((E2^2-E4)/f_inf)(infinity)
            -1/(2*d)

            sage: G = HeckeTriangleGroup(n=Infinity)
            sage: z = AlgebraicField()(1/10+13/10*I)
            sage: A = G.V(4)
            sage: S = G.S()
            sage: T = G.T()
            sage: A == (T*S)**3*T
            True
            sage: az = A.acton(z)
            sage: az == (A[0,0]*z + A[0,1]) / (A[1,0]*z + A[1,1])
            True

            sage: f_i(z)
            0.6208853409... - 0.1212525492...*I
            sage: f_i(az)
            6.103314419... + 20.42678597...*I
            sage: k = f_i.weight()
            sage: aut_fact = f_i.ep()^3 * (((T*S)**2*T).acton(z)/AlgebraicField()(i))**k * (((T*S)*T).acton(z)/AlgebraicField()(i))**k * (T.acton(z)/AlgebraicField()(i))**k
            sage: abs(aut_fact - f_i.parent().aut_factor(A, z)) < 1e-12
            True
            sage: aut_fact * f_i(z)
            6.103314419... + 20.42678597...*I

            sage: f_i.parent().default_num_prec(1000)
            sage: f_i.parent().default_prec(300)
            sage: (f_i.q_expansion_fixed_d().polynomial())(exp((2*pi*i).n(1000)*z/G.lam()))    # long time
            0.620885340917559158572271... - 0.121252549240996430425967...*I
            sage: (f_i.q_expansion_fixed_d().polynomial())(exp((2*pi*i).n(1000)*az/G.lam()))    # long time
            6.10331441975198186745017... + 20.4267859728657976382684...*I

            sage: f = f_i*E2
            sage: f(z)
            0.5349190275... - 0.1322370856...*I
            sage: f(az)
            -140.4711702... + 469.0793692...*I
            sage: k = f.weight()
            sage: aut_fact = f.ep()^3 * (((T*S)**2*T).acton(z)/AlgebraicField()(i))**k * (((T*S)*T).acton(z)/AlgebraicField()(i))**k * (T.acton(z)/AlgebraicField()(i))**k
            sage: abs(aut_fact - f.parent().aut_factor(A, z)) < 1e-12
            True
            sage: k2 = f_i.weight()
            sage: aut_fact2 = f_i.ep() * (((T*S)**2*T).acton(z)/AlgebraicField()(i))**k2 * (((T*S)*T).acton(z)/AlgebraicField()(i))**k2 * (T.acton(z)/AlgebraicField()(i))**k2
            sage: abs(aut_fact2 - f_i.parent().aut_factor(A, z)) < 1e-12
            True
            sage: cor_term = (4 * A.c() * (A.c()*z+A.d())) / (2*pi*i).n(1000) * G.lam()
            sage: aut_fact*f(z) + cor_term*aut_fact2*f_i(z)
            -140.4711702... + 469.0793692...*I

            sage: f.parent().default_num_prec(1000)
            sage: f.parent().default_prec(300)
            sage: (f.q_expansion_fixed_d().polynomial())(exp((2*pi*i).n(1000)*z/G.lam()))    # long time
            0.534919027587592616802582... - 0.132237085641931661668338...*I

            sage: (f.q_expansion_fixed_d().polynomial())(exp((2*pi*i).n(1000)*az/G.lam()))    # long time
            -140.471170232432551196978... + 469.079369280804086032719...*I

        It is possible to evaluate at points of ``HyperbolicPlane()``::

            sage: p = HyperbolicPlane().PD().get_point(-I/2)
            sage: bool(p.to_model('UHP').coordinates() == I/3)
            True
            sage: E4(p) == E4(I/3)
            True
            sage: p = HyperbolicPlane().PD().get_point(I)
            sage: f_inf(p, check=True) == 0
            True
            sage: (1/(E2^2-E4))(p) == infinity
            True
        """

        i = QuadraticField(-1, 'I').gen()

        # if tau is a point of HyperbolicPlane then we use it's coordinates in the UHP model
        if (tau in HyperbolicPlane()):
           tau = tau.to_model('UHP').coordinates()

        if (prec == None):
            prec = self.parent().default_prec()
        if (num_prec == None):
            num_prec = self.parent().default_num_prec()

        # In case the order is known
        try:
            if (check or\
                    tau == infinity or\
                    tau == i or\
                    tau == self.group().rho() or\
                    tau == -self.group().rho().conjugate()):
                order_tau = self.order_at(tau)

                if (order_tau > 0):
                    return ZZ(0)
                elif (order_tau < 0):
                    return infinity
                elif (tau == infinity):
                    return self.q_expansion(prec=1)[0]
        except (TypeError, NotImplementedError):
            pass

        # The general case
        num_prec = max(\
            ZZ(getattr(tau,'prec',lambda: num_prec)()),\
            num_prec\
        )
        tau = tau.n(num_prec)
        (x,y,z,d) = self.parent().rat_field().gens()

        if (self.is_homogeneous() and self.is_modular()):
            q_exp = self.q_expansion_fixed_d(prec=prec, d_num_prec=num_prec)
            (A, w) = self.group().get_FD(tau)
            aut_factor = self.reduce(force=True).parent().aut_factor(A, w)
            if (type(q_exp) is LaurentSeries):
                return q_exp.laurent_polynomial()(exp((2 * pi * i).n(num_prec) / self.group().lam() * w)) * aut_factor
            else:
                return q_exp.polynomial()(exp((2 * pi * i).n(num_prec) / self.group().lam() * w)) * aut_factor
        elif (self._rat == z):
            E2 = self.parent().graded_ring().E2().reduce(force=True)
            (A, w) = self.group().get_FD(tau)
            aut_factor = E2.parent().aut_factor(A, w)
            E2_wvalue = E2.q_expansion_fixed_d(prec=prec, d_num_prec=num_prec).polynomial()(exp((2 * pi * i).n(num_prec) / self.group().lam() * w))
            if (self.hecke_n() == infinity):
                E2_cor_term = 4 * self.group().lam() / (2*pi*i).n(num_prec) * A.c() * (A.c()*w + A.d())
            else:
                E2_cor_term = 4 * self.group().lam() / (2*pi*i).n(num_prec) * self.hecke_n() / (self.hecke_n()-2) * A.c() * (A.c()*w + A.d())
            return E2_wvalue*aut_factor + E2_cor_term
        else:
            f_i   = self.parent().graded_ring().f_i()
            E2    = self.parent().graded_ring().E2()
            dval  = self.parent().group().dvalue().n(num_prec)
            if (self.hecke_n() == infinity):
                E4 = self.parent().graded_ring().E4()
                return self._rat.subs(x=E4(tau), y=f_i(tau), z=E2(tau), d=dval)
            else:
                f_rho = self.parent().graded_ring().f_rho()
                return self._rat.subs(x=f_rho(tau), y=f_i(tau), z=E2(tau), d=dval)

    def __call__(self, tau, prec = None, num_prec = None, check=False):
        r"""
        Try to return ``self`` evaluated at a point ``tau``
        in the upper half plane, where ``self`` is interpreted
        as a function in ``tau``, where ``q=exp(2*pi*i*tau)``.

        See :meth:`.evaluate` for more details.

        EXAMPLES::

            sage: from sage.modular.modform_hecketriangle.graded_ring import QuasiMeromorphicModularFormsRing
            sage: E4 = QuasiMeromorphicModularFormsRing(n=5, red_hom=True).E4().full_reduce()
            sage: z = -1/(-1/(2*i+30)-1)
            sage: E4(z)
            32288.05588811... - 118329.8566016...*I
            sage: E4(z) == E4.evaluate(z)
            True
        """

        return self.evaluate(tau, prec, num_prec, check)
