### 5.21.24 Rewrite an expression with different options : convert convertir

convert takes two arguments an expression and an option.
convert rewrites this expression applying rules depending on the option. Valid options are :

- sin converts an expression like trigsin.
- cos converts an expression like trigcos.
- sincos converts an expression like sincos.
- trig converts an expression like sincos.
- tan converts an expression like halftan.
- exp converts an expression like trig2exp.
- ln converts an expression like trig2exp.
- expln converts an expression like trig2exp.
- string converts an expression into a string.
- matrix converts a list of lists into a matrix.
- polynom converts a Taylor series into a polynomial by removing the remainder (cf 5.25.22).
- parfrac or partfrac or fullparfrac converts a rational fraction into its partial fraction decomposition (5.29.9).

convert can also :

- convert units, for example convert(1000_g,_kg)=1.0_kg (cf 8.1.4).
- write a real as a continued fraction : convert(a,confrac,’fc’) writes a as a continued fraction stored in fc. Do not forget to quote the last argument if it was assigned.
  For example, convert(1.2,confrac,’fc’)=[1,5] and fc contains the continued fraction equal to 1.2 (cf 5.8.7).
- transform an integer into the list of its digits in a base, beginning with the units digit (and reciprocally)
  - convert(n,base,b) transforms the integer n into the list of its digits in base b beginning with the units digit.
    For example, convert(123,base,10)=[3,2,1] and reciprocally
  - convert(l,base,b) transforms the list l into the integer n which has l as list of its digits in base b beginning with the units digit.
    For example, convert([3,2,1],base,10)=123 (cf 5.5).