Function: numerator
Section: conversions
C-Name: numerator
Prototype: GDG
Help: numerator(f,{D}): numerator of f.
Doc:
 numerator of $f$. This is defined as \kbd{f * denominator(f,D)}, see
 \kbd{denominator} for details. The optional argument $D$ allows to control
 over which ring we compute the denominator:

 \item $1$: we only consider the underlying $\Q$-structure and the
 denominator is a (positive) rational integer

 \item a simple variable, say \kbd{'x}: entries are considered as rational
 functions in $K(x)$ and the denominator is a polynomial in $x$.

 \bprog
 ? f = x + 1/y + 1/2;
 ? numerator(f) \\ a t_POL in x
 %2 = x + ((y + 2)/(2*y))
 ? numerator(f, 1) \\ Q-denominator is 2
 %3 = x + ((y + 2)/y)
 ? numerator(f, y) \\ as a rational function in y
 %5 = 2*y*x + (y + 2)
 @eprog
Variant: Also available are
 \fun{GEN}{numer}{GEN x}  which implements the not very useful default
 behaviour ($D$ is \kbd{NULL}) and
 \fun{GEN}{Q_remove_denom}{GEN x, GEN *ptd} ($D = 1$) and also returns the
 denominator (coding $1$ as \kbd{NULL}).
