r"""
Hecke triangle groups

AUTHORS:

- Jonas Jermann (2013): initial version

"""

#*****************************************************************************
#       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 __future__ import print_function
from __future__ import absolute_import

from sage.rings.all import ZZ, QQ, AA, AlgebraicField, infinity, PolynomialRing, NumberField
from sage.functions.all import cos,exp,sec
from sage.functions.other import psi1
from sage.symbolic.all import pi,i
from sage.matrix.constructor import matrix
from sage.misc.latex import latex
from sage.misc.misc_c import prod

from sage.groups.matrix_gps.finitely_generated import FinitelyGeneratedMatrixGroup_generic
from sage.structure.unique_representation import UniqueRepresentation
from sage.misc.cachefunc import cached_method

from .hecke_triangle_group_element import HeckeTriangleGroupElement, cyclic_representative, coerce_AA

class HeckeTriangleGroup(FinitelyGeneratedMatrixGroup_generic, UniqueRepresentation):
    r"""
    Hecke triangle group (2, n, infinity).
    """

    Element = HeckeTriangleGroupElement

    @staticmethod
    def __classcall__(cls, n=3):
        r"""
        Return a (cached) instance with canonical parameters.

        EXAMPLES::

            sage: from sage.modular.modform_hecketriangle.hecke_triangle_groups import HeckeTriangleGroup
            sage: HeckeTriangleGroup(QQ(3)) == HeckeTriangleGroup(int(3))
            True
        """

        if (n == infinity):
            n = infinity
        else:
            n = ZZ(n)
            if (n < 3):
                raise AttributeError("n has to be infinity or an Integer >= 3.")

        return super(HeckeTriangleGroup, cls).__classcall__(cls, n)

    def __init__(self, n):
        r"""
        Hecke triangle group (2, n, infinity).
        Namely the von Dyck group corresponding to the triangle group
        with angles (pi/2, pi/n, 0).

        INPUT:

        - ``n``   - ``infinity`` or an integer greater or equal to ``3``.

        OUTPUT:

        The Hecke triangle group for the given parameter ``n``.

        EXAMPLES::

            sage: from sage.modular.modform_hecketriangle.hecke_triangle_groups import HeckeTriangleGroup
            sage: G = HeckeTriangleGroup(12)
            sage: G
            Hecke triangle group for n = 12
            sage: G.category()
            Category of groups
        """

        self._n = n
        self.element_repr_method("default")

        if n in [3, infinity]:
            self._base_ring = ZZ
            self._lam = ZZ(1) if n==3 else ZZ(2)
        else:
            lam_symbolic = 2*cos(pi/n)
            K = NumberField(self.lam_minpoly(), 'lam', embedding = coerce_AA(lam_symbolic))
            #self._base_ring = K.order(K.gens())
            self._base_ring = K.maximal_order()
            self._lam = self._base_ring.gen(1)

        T = matrix(self._base_ring, [[1,self._lam],[0,1]])
        S = matrix(self._base_ring, [[0,-1],[1,0]])

        FinitelyGeneratedMatrixGroup_generic.__init__(self, ZZ(2), self._base_ring, [S, T])

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

        EXAMPLES::

            sage: from sage.modular.modform_hecketriangle.hecke_triangle_groups import HeckeTriangleGroup
            sage: HeckeTriangleGroup(10)
            Hecke triangle group for n = 10
        """

        return "Hecke triangle group for n = {}".format(self._n)

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

        EXAMPLES::

            sage: from sage.modular.modform_hecketriangle.hecke_triangle_groups import HeckeTriangleGroup
            sage: a = HeckeTriangleGroup(5)
            sage: latex(a)
            \Gamma^{(5)}
        """

        return '\\Gamma^{(%s)}'%(latex(self._n))

    def element_repr_method(self, method=None):
        r"""
        Either return or set the representation method for elements of ``self``.

        INPUT:

        - ``method``  -- If ``method=None`` (default) the current default representation
                         method is returned. Otherwise the default method is set to ``method``.
                         If ``method`` is not available a ValueError is raised. Possible methods are:

                         ``default``: Use the usual representation method for matrix group elements.

                         ``basic``:   The representation is given as a word in ``S`` and powers of ``T``.

                         ``conj``:    The conjugacy representative of the element is represented
                                      as a word in powers of the basic blocks, together with
                                      an unspecified conjugation matrix.

                         ``block``:   Same as ``conj`` but the conjugation matrix is specified as well.

        EXAMPLES::

            sage: from sage.modular.modform_hecketriangle.hecke_triangle_groups import HeckeTriangleGroup
            sage: G = HeckeTriangleGroup(5)
            sage: G.element_repr_method()
            'default'
            sage: G.element_repr_method("basic")
            sage: G.element_repr_method()
            'basic'
        """

        if method is None:
            return self._element_repr_method
        elif method in ["default", "basic", "block", "conj"]:
            self._element_repr_method=method
        else:
            raise ValueError("The specified method {} is not supported!").format(method)

    def one(self):
        r"""
        Return the identity element/matrix for ``self``.

        EXAMPLES::

            sage: from sage.modular.modform_hecketriangle.hecke_triangle_groups import HeckeTriangleGroup
            sage: G = HeckeTriangleGroup(10)
            sage: G(1) == G.one()
            True
            sage: G(1)
            [1 0]
            [0 1]

            sage: G(1).parent()
            Hecke triangle group for n = 10
        """

        return self.I()

    def lam_minpoly(self):
        r"""
        Return the minimal polynomial of the corresponding lambda parameter of ``self``.

        EXAMPLES::

            sage: from sage.modular.modform_hecketriangle.hecke_triangle_groups import HeckeTriangleGroup
            sage: HeckeTriangleGroup(10).lam_minpoly()
            x^4 - 5*x^2 + 5
            sage: HeckeTriangleGroup(17).lam_minpoly()
            x^8 - x^7 - 7*x^6 + 6*x^5 + 15*x^4 - 10*x^3 - 10*x^2 + 4*x + 1
            sage: HeckeTriangleGroup(infinity).lam_minpoly()
            x - 2
        """

        # TODO: Write an explicit (faster) implementation
        lam_symbolic = 2*cos(pi/self._n)
        return coerce_AA(lam_symbolic).minpoly()

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

        EXAMPLES::

            sage: from sage.modular.modform_hecketriangle.hecke_triangle_groups import HeckeTriangleGroup
            sage: HeckeTriangleGroup(n=infinity).base_ring()
            Integer Ring
            sage: HeckeTriangleGroup(n=7).base_ring()
            Maximal Order in Number Field in lam with defining polynomial x^3 - x^2 - 2*x + 1
        """

        return self._base_ring

    def base_field(self):
        r"""
        Return the base field of ``self``.

        EXAMPLES::

            sage: from sage.modular.modform_hecketriangle.hecke_triangle_groups import HeckeTriangleGroup
            sage: HeckeTriangleGroup(n=infinity).base_field()
            Rational Field
            sage: HeckeTriangleGroup(n=7).base_field()
            Number Field in lam with defining polynomial x^3 - x^2 - 2*x + 1
        """

        if self._n in [3, infinity]:
            return QQ
        else:
            return self._base_ring.number_field()

    def n(self):
        r"""
        Return the parameter ``n`` of ``self``, where
        ``pi/n`` is the angle at ``rho`` of the corresponding
        basic hyperbolic triangle with vertices ``i``, ``rho``
        and ``infinity``.

        EXAMPLES::

            sage: from sage.modular.modform_hecketriangle.hecke_triangle_groups import HeckeTriangleGroup
            sage: HeckeTriangleGroup(10).n()
            10
            sage: HeckeTriangleGroup(infinity).n()
            +Infinity
        """

        return self._n

    # TODO: rename this to a more descriptive lambda in a later update/patch
    def lam(self):
        r"""
        Return the parameter ``lambda`` of ``self``,
        where ``lambda`` is twice the real part of ``rho``,
        lying between ``1`` (when ``n=3``) and ``2`` (when ``n=infinity``).

        EXAMPLES::

            sage: from sage.modular.modform_hecketriangle.hecke_triangle_groups import HeckeTriangleGroup
            sage: HeckeTriangleGroup(3).lam()
            1
            sage: HeckeTriangleGroup(4).lam()
            lam
            sage: HeckeTriangleGroup(4).lam()^2
            2
            sage: HeckeTriangleGroup(6).lam()^2
            3
            sage: AA(HeckeTriangleGroup(10).lam())
            1.9021130325903...?
            sage: HeckeTriangleGroup(infinity).lam()
            2
        """

        return self._lam

    def rho(self):
        r"""
        Return the vertex ``rho`` of the basic hyperbolic
        triangle which describes ``self``. ``rho`` has
        absolute value 1 and angle ``pi/n``.

        EXAMPLES::

            sage: from sage.modular.modform_hecketriangle.hecke_triangle_groups import HeckeTriangleGroup
            sage: HeckeTriangleGroup(3).rho() == QQbar(1/2 + sqrt(3)/2*i)
            True
            sage: HeckeTriangleGroup(4).rho() == QQbar(sqrt(2)/2*(1 + i))
            True
            sage: HeckeTriangleGroup(6).rho() == QQbar(sqrt(3)/2 + 1/2*i)
            True
            sage: HeckeTriangleGroup(10).rho()
            0.95105651629515...? + 0.30901699437494...?*I
            sage: HeckeTriangleGroup(infinity).rho()
            1
        """

        # TODO: maybe rho should be replaced by -rhobar
        # Also we could use NumberFields...
        if (self._n == infinity):
            return coerce_AA(1)
        else:
            rho = AlgebraicField()(exp(pi/self._n*i))
            rho.simplify()

            return rho

    def alpha(self):
        r"""
        Return the parameter ``alpha`` of ``self``.
        This is the first parameter of the hypergeometric series used
        in the calculation of the Hauptmodul of ``self``.

        EXAMPLES::

            sage: from sage.modular.modform_hecketriangle.hecke_triangle_groups import HeckeTriangleGroup
            sage: HeckeTriangleGroup(3).alpha()
            1/12
            sage: HeckeTriangleGroup(4).alpha()
            1/8
            sage: HeckeTriangleGroup(5).alpha()
            3/20
            sage: HeckeTriangleGroup(6).alpha()
            1/6
            sage: HeckeTriangleGroup(10).alpha()
            1/5
            sage: HeckeTriangleGroup(infinity).alpha()
            1/4
        """

        return ZZ(1)/ZZ(2) * (ZZ(1)/ZZ(2) - ZZ(1)/self._n)

    def beta(self):
        r"""
        Return the parameter ``beta`` of ``self``.
        This is the second parameter of the hypergeometric series used
        in the calculation of the Hauptmodul of ``self``.

        EXAMPLES::

            sage: from sage.modular.modform_hecketriangle.hecke_triangle_groups import HeckeTriangleGroup
            sage: HeckeTriangleGroup(3).beta()
            5/12
            sage: HeckeTriangleGroup(4).beta()
            3/8
            sage: HeckeTriangleGroup(5).beta()
            7/20
            sage: HeckeTriangleGroup(6).beta()
            1/3
            sage: HeckeTriangleGroup(10).beta()
            3/10
            sage: HeckeTriangleGroup(infinity).beta()
            1/4
        """

        return ZZ(1)/ZZ(2) * (ZZ(1)/ZZ(2) + ZZ(1)/self._n)

    # We use cached method here to create unique instances of basic matrices
    # (major performance gain)
    @cached_method
    def I(self):
        r"""
        Return the identity element/matrix for ``self``.

        EXAMPLES::

            sage: from sage.modular.modform_hecketriangle.hecke_triangle_groups import HeckeTriangleGroup
            sage: HeckeTriangleGroup(10).I()
            [1 0]
            [0 1]

            sage: HeckeTriangleGroup(10).I().parent()
            Hecke triangle group for n = 10
        """

        return self(matrix(self._base_ring, [[1,0],[0,1]]), check=False)

    # We use cached method here to create unique instances of basic matrices
    # (major performance gain)
    @cached_method
    def T(self, m=1):
        r"""
        Return the element in ``self`` corresponding to the translation by ``m*self.lam()``.

        INPUT:

        - ``m`` -- An integer, default: ``1``, namely the second generator of ``self``.

        EXAMPLES::

            sage: from sage.modular.modform_hecketriangle.hecke_triangle_groups import HeckeTriangleGroup
            sage: HeckeTriangleGroup(3).T()
            [1 1]
            [0 1]
            sage: HeckeTriangleGroup(10).T(-4)
            [     1 -4*lam]
            [     0      1]
            sage: HeckeTriangleGroup(10).T().parent()
            Hecke triangle group for n = 10
        """

        return self(matrix(self._base_ring, [[1,self._lam*m],[0,1]]), check=False)

    # We use cached method here to create unique instances of basic matrices
    # (major performance gain)
    @cached_method
    def S(self):
        r"""
        Return the generator of ``self`` corresponding to the
        conformal circle inversion.

        EXAMPLES::

            sage: from sage.modular.modform_hecketriangle.hecke_triangle_groups import HeckeTriangleGroup
            sage: HeckeTriangleGroup(3).S()
            [ 0 -1]
            [ 1  0]
            sage: HeckeTriangleGroup(10).S()
            [ 0 -1]
            [ 1  0]
            sage: HeckeTriangleGroup(10).S()^2 == -HeckeTriangleGroup(10).I()
            True
            sage: HeckeTriangleGroup(10).S()^4 == HeckeTriangleGroup(10).I()
            True

            sage: HeckeTriangleGroup(10).S().parent()
            Hecke triangle group for n = 10
        """

        return self.gen(0)

    # We use cached method here to create unique instances of basic matrices
    # (major performance gain)
    @cached_method
    def U(self):
        r"""
        Return an alternative generator of ``self`` instead of ``T``.
        ``U`` stabilizes ``rho`` and has order ``2*self.n()``.

        If ``n=infinity`` then ``U`` is parabolic and has infinite order,
        it then fixes the cusp ``[-1]``.

        EXAMPLES::

            sage: from sage.modular.modform_hecketriangle.hecke_triangle_groups import HeckeTriangleGroup
            sage: HeckeTriangleGroup(3).U()
            [ 1 -1]
            [ 1  0]
            sage: HeckeTriangleGroup(3).U()^3 == -HeckeTriangleGroup(3).I()
            True
            sage: HeckeTriangleGroup(3).U()^6 == HeckeTriangleGroup(3).I()
            True
            sage: HeckeTriangleGroup(10).U()
            [lam  -1]
            [  1   0]
            sage: HeckeTriangleGroup(10).U()^10 == -HeckeTriangleGroup(10).I()
            True
            sage: HeckeTriangleGroup(10).U()^20 == HeckeTriangleGroup(10).I()
            True

            sage: HeckeTriangleGroup(10).U().parent()
            Hecke triangle group for n = 10
        """

        return self.T() * self.S()

    def V(self, j):
        r"""
        Return the j'th generator for the usual representatives of
        conjugacy classes of ``self``. It is given by ``V=U^(j-1)*T``.

        INPUT:

        - ``j``  -- Any integer. To get the usual representatives
                    ``j`` should range from ``1`` to ``self.n()-1``.

        OUTPUT:

        The corresponding matrix/element.
        The matrix is parabolic if ``j`` is congruent to +-1 modulo ``self.n()``.
        It is elliptic if ``j`` is congruent to 0 modulo ``self.n()``.
        It is hyperbolic otherwise.

        EXAMPLES::

            sage: from sage.modular.modform_hecketriangle.hecke_triangle_groups import HeckeTriangleGroup
            sage: G = HeckeTriangleGroup(3)
            sage: G.V(0) == -G.S()
            True
            sage: G.V(1) == G.T()
            True
            sage: G.V(2)
            [1 0]
            [1 1]
            sage: G.V(3) == G.S()
            True

            sage: G = HeckeTriangleGroup(5)
            sage: G.element_repr_method("default")
            sage: G.V(1)
            [  1 lam]
            [  0   1]
            sage: G.V(2)
            [lam lam]
            [  1 lam]
            sage: G.V(3)
            [lam   1]
            [lam lam]
            sage: G.V(4)
            [  1   0]
            [lam   1]
            sage: G.V(5) == G.S()
            True
        """

        return self.U()**(j-1) * self.T()

    def dvalue(self):
        r"""
        Return a symbolic expression (or an exact value in case n=3, 4, 6)
        for the transfinite diameter (or capacity) of ``self``.
        I.e. the first nontrivial Fourier coefficient of the Hauptmodul
        for the Hecke triangle group in case it is normalized to ``J_inv(i)=1``.

        EXAMPLES::

            sage: from sage.modular.modform_hecketriangle.hecke_triangle_groups import HeckeTriangleGroup
            sage: HeckeTriangleGroup(3).dvalue()
            1/1728
            sage: HeckeTriangleGroup(4).dvalue()
            1/256
            sage: HeckeTriangleGroup(5).dvalue()
            e^(2*euler_gamma - 4*pi/(sqrt(5) + 1) + psi(17/20) + psi(13/20))
            sage: HeckeTriangleGroup(6).dvalue()
            1/108
            sage: HeckeTriangleGroup(10).dvalue()
            e^(2*euler_gamma - 4*pi/sqrt(2*sqrt(5) + 10) + psi(4/5) + psi(7/10))
            sage: HeckeTriangleGroup(infinity).dvalue()
            1/64
        """

        n = self._n
        if (n==3):
            return ZZ(1)/ZZ(2**6*3**3)
        elif (n==4):
            return ZZ(1)/ZZ(2**8)
        elif (n==6):
            return ZZ(1)/ZZ(2**2*3**3)
        elif (n==infinity):
            return ZZ(1)/ZZ(2**6)
        else:
            return exp(-ZZ(2)*psi1(ZZ(1)) + psi1(ZZ(1)-self.alpha())+psi1(ZZ(1)-self.beta()) - pi*sec(pi/self._n))


    def is_arithmetic(self):
        r"""
        Return True if ``self`` is an arithmetic subgroup.

        EXAMPLES::

            sage: from sage.modular.modform_hecketriangle.hecke_triangle_groups import HeckeTriangleGroup
            sage: HeckeTriangleGroup(3).is_arithmetic()
            True
            sage: HeckeTriangleGroup(4).is_arithmetic()
            True
            sage: HeckeTriangleGroup(5).is_arithmetic()
            False
            sage: HeckeTriangleGroup(6).is_arithmetic()
            True
            sage: HeckeTriangleGroup(10).is_arithmetic()
            False
            sage: HeckeTriangleGroup(infinity).is_arithmetic()
            True
        """

        if (self._n in [ZZ(3), ZZ(4), ZZ(6), infinity]):
            return True
        else:
            return False

    def get_FD(self, z):
        r"""
        Return a tuple (A,w) which determines how to map ``z``
        to the usual (strict) fundamental domain of ``self``.

        INPUT:

        - ``z`` -- a complex number or an element of AlgebraicField().

        OUTPUT:

        A tuple ``(A, w)``.

        - ``A`` -- a matrix in ``self`` such that ``A.acton(w)==z``
          (if ``z`` is exact at least).

        - ``w`` -- a complex number or an element of AlgebraicField()
          (depending on the type ``z``) which lies inside the (strict)
          fundamental domain of ``self`` (``self.in_FD(w)==True``) and
          which is equivalent to ``z`` (by the above property).

        EXAMPLES::

            sage: from sage.modular.modform_hecketriangle.hecke_triangle_groups import HeckeTriangleGroup
            sage: G = HeckeTriangleGroup(8)
            sage: z = AlgebraicField()(1+i/2)
            sage: (A, w) = G.get_FD(z)
            sage: A
            [-lam    1]
            [  -1    0]
            sage: A.acton(w) == z
            True

            sage: from sage.modular.modform_hecketriangle.space import ModularForms
            sage: z = (134.12 + 0.22*i).n()
            sage: (A, w) = G.get_FD(z)
            sage: A
            [-73*lam^3 + 74*lam       73*lam^2 - 1]
            [        -lam^2 + 1                lam]
            sage: w
            0.769070776942... + 0.779859114103...*I
            sage: z
            134.120000000... + 0.220000000000...*I
            sage: A.acton(w)
            134.1200000... + 0.2200000000...*I
        """

        ID = self.I()
        T  = self.T()
        S  = self.S()
        TI = self.T(-1)

        A = ID
        w = z
        while (abs(w) < ZZ(1) or abs(w.real()) > self.lam()/ZZ(2)):
            if (abs(w) < ZZ(1)):
                w = self.S().acton(w)
                A = S*A
            while (w.real() >= self.lam()/ZZ(2)):
                w = TI.acton(w)
                A = TI*A
            while (w.real() < -self.lam()/ZZ(2)):
                w = T.acton(w)
                A = T*A
        if (w.real() == self.lam()/ZZ(2)):
            w = TI.acton(w)
            A = TI*A
        if (abs(w) == ZZ(1) and w.real() > ZZ(0)):
            w = S.acton(w)
            A = S*A

        AI = A.inverse()

        return (AI, A.acton(z))

    def in_FD(self, z):
        r"""
        Returns ``True`` if ``z`` lies in the (strict) fundamental
        domain of ``self``.

        EXAMPLES::

            sage: from sage.modular.modform_hecketriangle.hecke_triangle_groups import HeckeTriangleGroup
            sage: HeckeTriangleGroup(5).in_FD(CC(1.5/2 + 0.9*i))
            True
            sage: HeckeTriangleGroup(4).in_FD(CC(1.5/2 + 0.9*i))
            False
        """

        return self.get_FD(z)[0] == self.I()

    def root_extension_field(self, D):
        r"""
        Return the quadratic extension field of the base field by
        the square root of the given discriminant ``D``.

        INPUT:

        - ``D`` -- An element of the base ring of ``self``
                   corresponding to a discriminant.

        OUTPUT:

        A relative (at most quadratic) extension to the base field
        of self in the variable ``e`` which corresponds to ``sqrt(D)``.
        If the extension degree is ``1`` then the base field is returned.

        The correct embedding is the positive resp. positive imaginary one.
        Unfortunately no default embedding can be specified for relative
        number fields yet.

        EXAMPLES::

            sage: from sage.modular.modform_hecketriangle.hecke_triangle_groups import HeckeTriangleGroup
            sage: G = HeckeTriangleGroup(n=infinity)
            sage: G.root_extension_field(32)
            Number Field in e with defining polynomial x^2 - 32
            sage: G.root_extension_field(-4)
            Number Field in e with defining polynomial x^2 + 4
            sage: G.root_extension_field(4) == G.base_field()
            True

            sage: G = HeckeTriangleGroup(n=7)
            sage: lam = G.lam()
            sage: D = 4*lam^2 + 4*lam - 4
            sage: G.root_extension_field(D)
            Number Field in e with defining polynomial x^2 - 4*lam^2 - 4*lam + 4 over its base field
            sage: G.root_extension_field(4) == G.base_field()
            True
            sage: D = lam^2 - 4
            sage: G.root_extension_field(D)
            Number Field in e with defining polynomial x^2 - lam^2 + 4 over its base field
        """

        K = self.base_field()
        x = PolynomialRing(K, 'x').gen()
        D = self.base_ring()(D)

        if D.is_square():
            return K
        else:
            # unfortunately we can't set embeddings for relative extensions :-(
            # return K.extension(x**2 - D, 'e', embedding=AA(D).sqrt())

            L = K.extension(x**2 - D, 'e')

            #e = AA(D).sqrt()
            #emb = L.hom([e])
            #L._unset_embedding()
            #L.register_embedding(emb)

            #return NumberField(L.absolute_polynomial(), 'e', structure=AbsoluteFromRelative(L), embedding=(???))
            return L

    # We cache this method for performance reasons (it is repeatedly reused)
    @cached_method
    def root_extension_embedding(self, D, K=None):
        r"""
        Return the correct embedding from the root extension field
        of the given discriminant ``D``  to the field ``K``.

        Also see the method ``root_extension_embedding(K)`` of
        ``HeckeTriangleGroupElement`` for more examples.

        INPUT:

        - ``D`` -- An element of the base ring of ``self``
                   corresponding to a discriminant.

        - ``K`` -- A field to which we want the (correct) embeddding.
                   If ``K=None`` (default) then ``AlgebraicField()`` is
                   used for positive ``D`` and ``AlgebraicRealField()``
                   otherwise.

        OUTPUT:

        The corresponding embedding if it was found.
        Otherwise a ValueError is raised.

        EXAMPLES::

            sage: from sage.modular.modform_hecketriangle.hecke_triangle_groups import HeckeTriangleGroup
            sage: G = HeckeTriangleGroup(n=infinity)
            sage: G.root_extension_embedding(32)
            Ring morphism:
              From: Number Field in e with defining polynomial x^2 - 32
              To:   Algebraic Real Field
              Defn: e |--> 5.656854249492...?
            sage: G.root_extension_embedding(-4)
            Ring morphism:
              From: Number Field in e with defining polynomial x^2 + 4
              To:   Algebraic Field
              Defn: e |--> 2*I
            sage: G.root_extension_embedding(4)
            Ring Coercion morphism:
              From: Rational Field
              To:   Algebraic Real Field

            sage: G = HeckeTriangleGroup(n=7)
            sage: lam = G.lam()
            sage: D = 4*lam^2 + 4*lam - 4
            sage: G.root_extension_embedding(D, CC)
            Relative number field morphism:
              From: Number Field in e with defining polynomial x^2 - 4*lam^2 - 4*lam + 4 over its base field
              To:   Complex Field with 53 bits of precision
              Defn: e |--> 4.02438434522...
                    lam |--> 1.80193773580...
            sage: D = lam^2 - 4
            sage: G.root_extension_embedding(D)
            Relative number field morphism:
              From: Number Field in e with defining polynomial x^2 - lam^2 + 4 over its base field
              To:   Algebraic Field
              Defn: e |--> 0.?... + 0.867767478235...?*I
                    lam |--> 1.801937735804...?
        """

        D = self.base_ring()(D)
        F = self.root_extension_field(D)
        if K is None:
            if coerce_AA(D) > 0:
                K = AA
            else:
                K = AlgebraicField()

        L = [emb for emb in F.embeddings(K)]

        # Three possibilities up to numerical artefacts:
        # (1) emb = e, purely imaginary
        # (2) emb = e or lam (can't distinguish), purely real
        # (3) emb = (e,lam), e purely imaginary, lam purely real
        # (4) emb = (e,lam), e purely real, lam purely real
        # There always exists one emb with "e" positive resp. positive imaginary
        # and if there is a lam there exists a positive one...
        #
        # Criteria to pick the correct "maximum":
        # 1. First figure out if e resp. lam is purely real or imaginary
        #    (using "abs(e.imag()) > abs(e.real())")
        # 2. In the purely imaginary case we don't want anything negative imaginary
        #    and we know the positive case is unique after sorting lam
        # 3. For the remaining cases we want the biggest real part
        #    (and lam should get comparison priority)
        def emb_key(emb):
            L = []
            gens_len = len(emb.im_gens())
            for k in range(gens_len):
                a = emb.im_gens()[k]
                try:
                    a.simplify()
                    a.exactify()
                except AttributeError:
                    pass
                # If a is purely imaginary:
                if abs(a.imag()) > abs(a.real()):
                    if a.imag() < 0:
                        a = -infinity
                    else:
                        a = ZZ(0)
                else:
                    a = a.real()

                L.append(a)

            L.reverse()
            return L

        if len(L) > 1:
            L.sort(key = emb_key)
        return L[-1]

    def _elliptic_conj_reps(self):
        r"""
        Store all elliptic conjugacy representatives in the
        internal dictionary. This is a helper function
        used by :meth:`_conjugacy_representatives`.

        EXAMPLES::

            sage: from sage.modular.modform_hecketriangle.hecke_triangle_groups import HeckeTriangleGroup
            sage: G = HeckeTriangleGroup(n=5)
            sage: G.element_repr_method("conj")
            sage: G._elliptic_conj_reps()
            sage: sorted(G._conj_prim.items())
            [(-4, [[S], [S]]), (lam - 3, [[U], [U]]), (0, [[V(4)]])]
            sage: sorted(G._conj_nonprim.items())
            [(-lam - 2, [[U^(-2)], [U^2], [U^(-2)], [U^2]]), (lam - 3, [[U^(-1)], [U^(-1)]])]
        """
        if not hasattr(self, "_max_block_length"):
            self._conjugacy_representatives()
        elif ZZ(-4) in self._conj_prim:
            return

        D = self.U().discriminant()
        if D not in self._conj_prim:
            self._conj_prim[D] = []
        self._conj_prim[D].append(self.U())

        D = self.S().discriminant()
        if D not in self._conj_prim:
            self._conj_prim[D] = []
        self._conj_prim[D].append(self.S())

        other_reps = [self.U()**k for k in range(-((self.n()-1)/2).floor(), (self.n()/2).floor() + 1) if k not in [0,1]]

        for v in other_reps:
            D = v.discriminant()
            if D not in self._conj_nonprim:
                self._conj_nonprim[D] = []
            self._conj_nonprim[D].append(v)

    def _conjugacy_representatives(self, max_block_length=ZZ(0), D=None):
        r"""
        Store conjugacy representatives up to block length
        ``max_block_length`` (a non-negative integer, default: 0)
        in the internal dictionary. Previously calculated data is reused.
        This is a helper function for e.g. :meth:`class_number`.

        The set of all (hyperbolic) conjugacy types of block length
        ``t`` is stored in ``self._conj_block[t]``.
        The set of all primitive representatives (so far) with
        discriminant ``D`` is stored in ``self._conj_prim[D]``.
        The set of all non-primitive representatives (so far) with
        discriminant ``D`` is stored in ``self._conj_nonprim[D]``.

        The case of non-positive discriminants is done manually.

        INPUT:

        - ``max_block_length`` -- A non-negative integer (default: ``0``),
                                  the maximal block length.

        - ``D``                -- An element/discriminant of the base ring or
                                  more generally an upper bound for the
                                  involved discriminants. If ``D != None``
                                  then an upper bound for ``max_block_length``
                                  is deduced from ``D`` (default: ``None``).

        EXAMPLES::

            sage: from sage.modular.modform_hecketriangle.hecke_triangle_groups import HeckeTriangleGroup
            sage: G = HeckeTriangleGroup(n=5)
            sage: G.element_repr_method("conj")
            sage: G._conjugacy_representatives(2)

            sage: list(G._conj_block[2])
            [((4, 1), (3, 1)), ((2, 2),), ((3, 2),), ((3, 1), (1, 1)), ((4, 1), (1, 1)), ((4, 1), (2, 1)), ((3, 1), (2, 1)), ((2, 1), (1, 1))]

            sage: [key for key in sorted(G._conj_prim)]
            [-4, lam - 3, 0, 4*lam, 7*lam + 6, 9*lam + 5, 15*lam + 6, 33*lam + 21]
            sage: for key in sorted(G._conj_prim):
            ....:     print(G._conj_prim[key])
            [[S], [S]]
            [[U], [U]]
            [[V(4)]]
            [[V(3)], [V(2)]]
            [[V(1)*V(4)]]
            [[V(3)*V(4)], [V(1)*V(2)]]
            [[V(1)*V(3)], [V(2)*V(4)]]
            [[V(2)*V(3)]]
            sage: [key for key in sorted(G._conj_nonprim)]
            [-lam - 2, lam - 3, 32*lam + 16]

            sage: for key in sorted(G._conj_nonprim):
            ....:     print(G._conj_nonprim[key])
            [[U^(-2)], [U^2], [U^(-2)], [U^2]]
            [[U^(-1)], [U^(-1)]]
            [[V(2)^2], [V(3)^2]]

            sage: G.element_repr_method("default")
        """

        from sage.combinat.partition import OrderedPartitions
        from sage.combinat.combinat import tuples
        from sage.arith.all import divisors

        if not D is None:
            max_block_length = max(coerce_AA(0), coerce_AA((D + 4)/(self.lam()**2))).sqrt().floor()
        else:
            try:
                max_block_length = ZZ(max_block_length)
                if max_block_length < 0:
                    raise TypeError
            except TypeError:
                raise ValueError("max_block_length must be a non-negative integer!")

        if not hasattr(self, "_max_block_length"):
            self._max_block_length = ZZ(0)
            self._conj_block       = {}
            self._conj_nonprim     = {}
            self._conj_prim        = {}

            # It is not clear how to define the class number for D=0:
            # Conjugacy classes are V(n-1)^(+-k) for arbitrary k
            # and the trivial class (what about self_conj_block[0]?).
            #
            # One way is to define it using the fixed points and in
            # that case V(n-1) would be a good representative.
            # The non-primitive case is unclear however...
            #
            # We set it here to ensure that 0 is enlisted as a discriminant...
            #
            self._conj_prim[ZZ(0)] = []
            self._conj_prim[ZZ(0)].append(self.V(self.n()-1))

            self._elliptic_conj_reps()

        if max_block_length <= self._max_block_length:
            return

        def is_cycle(seq):
            length = len(seq)
            for n in divisors(length):
                if n < length and is_cycle_of_length(seq, n):
                    return True
            return False

        def is_cycle_of_length(seq, n):
            for i in range(n, len(seq)):
                if seq[i] != seq[i % n]:
                    return False
            return True

        j_list = range(1, self.n())

        for t in range(self._max_block_length + 1, max_block_length + 1):
            t_ZZ = ZZ(t)
            if t_ZZ not in self._conj_block:
                self._conj_block[t_ZZ] = set()

            partitions = OrderedPartitions(t).list()
            for par in partitions:
                len_par = len(par)
                exp_list = tuples(j_list, len_par)
                for ex in exp_list:
                    keep = True
                    if len_par > 1:
                        for k in range(-1,len_par-1):
                            if ex[k] == ex[k+1]:
                                keep = False
                                break
                    # We don't want powers of V(1)
                    elif ex[0] == 1:
                        keep = False
                    # But: Do we maybe want powers of V(n-1)??
                    # For now we exclude the parabolic cases...
                    elif ex[0] == self.n()-1:
                        keep = False

                    if keep:
                        conj_type = cyclic_representative(tuple((ZZ(ex[k]), ZZ(par[k])) for k in range(len_par)))
                        self._conj_block[t_ZZ].add(conj_type)

            for el in self._conj_block[t_ZZ]:
                group_el = prod([self.V(el[k][0])**el[k][1] for k in range(len(el))])

                #if el != group_el.conjugacy_type():
                #    raise AssertionError("This shouldn't happen!")

                D = group_el.discriminant()
                if coerce_AA(D) < 0:
                    raise AssertionError("This shouldn't happen!")
                if coerce_AA(D) == 0:
                    raise AssertionError("This shouldn't happen!")
                    #continue

                # The primitive cases
                #if group_el.is_primitive():
                if not ((len(el) == 1 and el[0][1] > 1) or is_cycle(el)):
                    if D not in self._conj_prim:
                        self._conj_prim[D] = []
                    self._conj_prim[D].append(group_el)
                # The remaining cases
                else:
                    if D not in self._conj_nonprim:
                        self._conj_nonprim[D] = []
                    self._conj_nonprim[D].append(group_el)

        self._max_block_length = max_block_length

    def class_representatives(self, D, primitive=True):
        r"""
        Return a representative for each conjugacy class for the
        discriminant ``D`` (ignoring the sign).

        If ``primitive=True`` only one representative for each
        fixed point is returned (ignoring sign).

        INPUT:

        - ``D``          -- An element of the base ring corresponding
                            to a valid discriminant.

        - ``primitive``  -- If ``True`` (default) then only primitive
                            representatives are considered.

        EXAMPLES::

            sage: from sage.modular.modform_hecketriangle.hecke_triangle_groups import HeckeTriangleGroup
            sage: G = HeckeTriangleGroup(n=4)
            sage: G.element_repr_method("conj")

            sage: R = G.class_representatives(4)
            sage: R
            [[V(2)]]
            sage: [v.continued_fraction()[1] for v in R]
            [(2,)]

            sage: R = G.class_representatives(0)
            sage: R
            [[V(3)]]
            sage: [v.continued_fraction()[1] for v in R]
            [(1, 2)]

            sage: R = G.class_representatives(-4)
            sage: R
            [[S]]
            sage: R = G.class_representatives(-4, primitive=False)
            sage: R
            [[S], [U^2]]

            sage: R = G.class_representatives(G.lam()^2 - 4)
            sage: R
            [[U]]
            sage: R = G.class_representatives(G.lam()^2 - 4, primitive=False)
            sage: R
            [[U], [U^(-1)]]

            sage: R = G.class_representatives(14)
            sage: R
            [[V(2)*V(3)], [V(1)*V(2)]]
            sage: [v.continued_fraction()[1] for v in R]
            [(1, 2, 2), (3,)]

            sage: R = G.class_representatives(32)
            sage: R
            [[V(3)^2*V(1)], [V(1)^2*V(3)]]
            sage: [v.continued_fraction()[1] for v in R]
            [(1, 2, 1, 3), (1, 4)]

            sage: R = G.class_representatives(32, primitive=False)
            sage: R
            [[V(3)^2*V(1)], [V(1)^2*V(3)], [V(2)^2]]

            sage: G.element_repr_method("default")
        """

        if coerce_AA(D) == 0 and not primitive:
            raise ValueError("There are infinitely many non-primitive conjugacy classes of discriminant 0.")

        self._conjugacy_representatives(D=D)

        L = []
        if D in self._conj_prim:
            L += self._conj_prim[D]
        if not primitive and D in self._conj_nonprim:
            L += self._conj_nonprim[D]

        if len(L) == 0:
            raise ValueError("D = {} is not a{} discriminant for {}".format(D, " primitive" if primitive else "", self))
        else:
            return L

    def class_number(self, D, primitive=True):
        r"""
        Return the class number of ``self`` for the discriminant ``D``.
        I.e. the number of conjugacy classes of (primitive) elements
        of discriminant ``D``.

        Note: Due to the 1-1 correspondence with hyperbolic fixed
        points resp. hyperbolic binary quadratic forms
        this also gives the class number in those cases.

        INPUT:

        - ``D``          -- An element of the base ring corresponding
                            to a valid discriminant.

        - ``primitive``  -- If ``True`` (default) then only primitive
                            elements are considered.

        EXAMPLES::

            sage: from sage.modular.modform_hecketriangle.hecke_triangle_groups import HeckeTriangleGroup
            sage: G = HeckeTriangleGroup(n=4)

            sage: G.class_number(4)
            1
            sage: G.class_number(4, primitive=False)
            1
            sage: G.class_number(14)
            2
            sage: G.class_number(32)
            2
            sage: G.class_number(32, primitive=False)
            3
            sage: G.class_number(68)
            4
        """

        if coerce_AA(D) <= 0:
            raise NotImplementedError

        self._conjugacy_representatives(D=D)

        num = ZZ(0)
        if D in self._conj_prim:
            num = len(self._conj_prim[D])
        if not primitive and D in self._conj_nonprim:
            num += len(self._conj_nonprim[D])

        if num == 0:
            raise ValueError("D = {} is not a{} discriminant for {}".format(D, " primitive" if primitive else "", self))
        else:
            return num

    def is_discriminant(self, D, primitive=True):
        r"""
        Returns whether ``D`` is a discriminant of an element of ``self``.

        Note: Checking that something isn't a discriminant takes much
        longer than checking for valid discriminants.

        INPUT:

        - ``D``          -- An element of the base ring.

        - ``primitive``  -- If ``True`` (default) then only primitive
                            elements are considered.

        OUTPUT:

        ``True`` if ``D`` is a primitive discriminant (a discriminant of
        a primitive element) and ``False`` otherwise.
        If ``primitive=False`` then also non-primitive elements are considered.

        EXAMPLES::

            sage: from sage.modular.modform_hecketriangle.hecke_triangle_groups import HeckeTriangleGroup
            sage: G = HeckeTriangleGroup(n=4)

            sage: G.is_discriminant(68)
            True
            sage: G.is_discriminant(196, primitive=False)    # long time
            True
            sage: G.is_discriminant(2)
            False
        """

        self._conjugacy_representatives(0)
        t_bound = max(coerce_AA(0), coerce_AA((D + 4)/(self.lam()**2))).sqrt().floor()
        for t in range(self._max_block_length + 1, t_bound + 1):
            self._conjugacy_representatives(t)

            if D in self._conj_prim:
                return True
            if not primitive and D in self._conj_nonprim:
                return True

        if D in self._conj_prim:
            return True
        elif not primitive and D in self._conj_nonprim:
            return True
        else:
            return False

    def list_discriminants(self, D, primitive=True, hyperbolic=True, incomplete=False):
        r"""
        Returns a list of all discriminants up to some upper bound ``D``.

        INPUT:

        - ``D``          -- An element/discriminant of the base ring or
                            more generally an upper bound for the discriminant.

        - ``primitive``  -- If ``True`` (default) then only primitive
                            discriminants are listed.

        - ``hyperbolic`` -- If ``True`` (default) then only positive
                            discriminants are listed.

        - ``incomplete`` -- If ``True`` (default: ``False``) then all (also higher)
                            discriminants which were gathered so far are listed
                            (however there might be missing discriminants inbetween).

        OUTPUT:

        A list of discriminants less than or equal to ``D``.

        EXAMPLES::

            sage: from sage.modular.modform_hecketriangle.hecke_triangle_groups import HeckeTriangleGroup
            sage: G = HeckeTriangleGroup(n=4)
            sage: G.list_discriminants(D=68)
            [4, 12, 14, 28, 32, 46, 60, 68]
            sage: G.list_discriminants(D=0, hyperbolic=False, primitive=False)
            [-4, -2, 0]

            sage: G = HeckeTriangleGroup(n=5)
            sage: G.list_discriminants(D=20)
            [4*lam, 7*lam + 6, 9*lam + 5]
            sage: G.list_discriminants(D=0, hyperbolic=False, primitive=False)
            [-4, -lam - 2, lam - 3, 0]
        """

        self._conjugacy_representatives(D=D)

        if incomplete:
            max_D = infinity
        else:
            max_D = coerce_AA(D)

        L = []
        if hyperbolic:
            L += [key for key in self._conj_prim if coerce_AA(key) > 0 and coerce_AA(key) <= max_D]
        else:
            L += [key for key in self._conj_prim if coerce_AA(key) <= max_D]

        if not primitive:
            if hyperbolic:
                L += [key for key in self._conj_nonprim if coerce_AA(key) > 0 and coerce_AA(key) <= max_D and key not in L]
            else:
                L += [key for key in self._conj_nonprim if coerce_AA(key) <= max_D and key not in L]

        return sorted(L, key=coerce_AA)

    # TODO: non-primitive ones?
    def reduced_elements(self, D):
        r"""
        Return all reduced (primitive) elements of discriminant ``D``.
        Also see the element method ``is_reduced()`` for more information.

        - ``D`` -- An element of the base ring corresponding
                   to a valid discriminant.

        EXAMPLES::

            sage: from sage.modular.modform_hecketriangle.hecke_triangle_groups import HeckeTriangleGroup
            sage: G = HeckeTriangleGroup(n=4)
            sage: R = G.reduced_elements(D=12)
            sage: R
            [
            [    5  -lam]  [     5 -3*lam]
            [3*lam    -1], [   lam     -1]
            ]
            sage: [v.continued_fraction() for v in R]
            [((), (1, 3)), ((), (3, 1))]
            sage: R = G.reduced_elements(D=14)
            sage: R
            [
            [ 5*lam     -3]  [ 5*lam     -7]  [4*lam    -3]  [3*lam    -1]
            [     7 -2*lam], [     3 -2*lam], [    3  -lam], [    1     0]
            ]
            sage: [v.continued_fraction() for v in R]
            [((), (1, 2, 2)), ((), (2, 2, 1)), ((), (2, 1, 2)), ((), (3,))]
        """

        L = self.class_representatives(D=D, primitive=True)
        R = []
        for v in L:
            R += v.reduced_elements()

        return R

    def simple_elements(self, D):
        r"""
        Return all simple elements of discriminant ``D``.
        Also see the element method ``is_simple()`` for more information.

        - ``D`` -- An element of the base ring corresponding
                   to a valid discriminant.

        EXAMPLES::

            sage: from sage.modular.modform_hecketriangle.hecke_triangle_groups import HeckeTriangleGroup
            sage: G = HeckeTriangleGroup(n=4)
            sage: G.simple_elements(D=12)
            [
            [  3 lam]  [  1 lam]
            [lam   1], [lam   3]
            ]
            sage: G.simple_elements(D=14)
            [
            [2*lam     1]  [  lam     1]  [2*lam     3]  [  lam     3]
            [    3   lam], [    3 2*lam], [    1   lam], [    1 2*lam]
            ]
        """

        L = self.class_representatives(D=D, primitive=True)
        R = []
        for v in L:
            R += v.simple_elements()

        return R

    def rational_period_functions(self, k, D):
        r"""
        Return a list of basic rational period functions of weight ``k`` for discriminant ``D``.
        The list is expected to be a generating set for all rational period functions of the
        given weight and discriminant (unknown).

        The method assumes that ``D > 0``.
        Also see the element method `rational_period_function` for more information.

        - ``k`` -- An even integer, the desired weight of the rational period functions.

        - ``D`` -- An element of the base ring corresponding
                   to a valid discriminant.

        EXAMPLES::

            sage: from sage.modular.modform_hecketriangle.hecke_triangle_groups import HeckeTriangleGroup
            sage: G = HeckeTriangleGroup(n=4)
            sage: G.rational_period_functions(k=4, D=12)
            [(z^4 - 1)/z^4]
            sage: G.rational_period_functions(k=-2, D=12)
            [-z^2 + 1, 4*lam*z^2 - 4*lam]
            sage: G.rational_period_functions(k=2, D=14)
            [(z^2 - 1)/z^2, 1/z, (24*z^6 - 120*z^4 + 120*z^2 - 24)/(9*z^8 - 80*z^6 + 146*z^4 - 80*z^2 + 9), (24*z^6 - 120*z^4 + 120*z^2 - 24)/(9*z^8 - 80*z^6 + 146*z^4 - 80*z^2 + 9)]
            sage: G.rational_period_functions(k=-4, D=14)
            [-z^4 + 1, 16*z^4 - 16, -16*z^4 + 16]
        """

        try:
            k = ZZ(k)
            if not ZZ(2).divides(k):
                raise TypeError
        except TypeError:
            raise ValueError("k={} has to be an even integer!".format(k))

        z = PolynomialRing(self.base_ring(), 'z').gen()

        R = []
        if k != 0:
            R.append(ZZ(1) - z**(-k))
        if k == 2:
            R.append(z**(-1))

        L = self.class_representatives(D=D, primitive=True)
        for v in L:
            rat = v.rational_period_function(k)
            if rat != 0:
                R.append(rat)

        return R
