Function: rnfidealup
Section: number_fields
C-Name: rnfidealup
Prototype: GG
Help: rnfidealup(rnf,x): lifts the ideal x (of the base field) to the
 relative field.
Doc: $\var{rnf}$ being a relative number
 field extension $L/K$ as output by \kbd{rnfinit} and $x$ being an ideal of
 $K$, gives the ideal $x\Z_L$ as an absolute ideal of $L/\Q$, in the form of a
 $\Z$-basis, given by a vector of polynomials (modulo \kbd{rnf.pol}).
 The following routine might be useful:
 \bprog
 \\ return y = rnfidealup(rnf,...) as an ideal in HNF form
 \\ associated to nf = nfinit( rnf.pol );
 idealgentoHNF(nf, y) = mathnf( Mat( matalgtobasis(nf, y) ) );
 @eprog
