Singular

D.2.12.14 preimageLoc

Usage:

preimageLoc ( ring_name, map_name, ideal_name );
all input parameters of type string

Return:

ideal

Purpose:

compute the preimage of an ideal under a given map for non-global orderings.
The 2nd argument has to be the name of a map from the basering to the given ring (or the name of an ideal defining such a map), and the ideal has to be an ideal in the given ring.

LIB "ring.lib";
ring S =0,(x,y,z),dp;
ring R0=0,(x,y,z),ds;
qring R=std(x+x2); if(voice>1) {export R;}
map psi=S,x,y,z;   if(voice>1) {export psi;}
ideal null;        if(voice>1) {export null;}
setring S;
ideal nu=preimageLoc("R","psi","null");
nu;
==> nu[1]=x