# Singular

##### 7.7.4.0. checkFactor
Procedure from library `dmod.lib` (see dmod_lib).

Usage:
checkFactor(I,f,qs [,eng]); I an ideal, f a poly, qs a poly, eng an optional int

Assume:
checkFactor is called from the basering, created by Sannfs-like proc,
that is, from the Weyl algebra in x1,..,xN,d1,..,dN tensored with K[s].
The ideal I is the annihilator of f^s in D[s], that is the ideal, computed
by Sannfs-like procedure (usually called LD there).
Moreover, f is a polynomial in K[x1,..,xN] and qs is a polynomial in K[s].

Return:
int, 1 if qs is a factor of the global Bernstein polynomial of f and 0 otherwise

Purpose:
check whether a univariate polynomial qs is a factor of the
Bernstein-Sato polynomial of f without explicit knowledge of the latter.

Note:
If eng <>0, `std` is used for Groebner basis computations,
otherwise (and by default) `slimgb` is used.

Display:
If printlevel=1, progress debug messages will be printed,
if printlevel>=2, all the debug messages will be printed.

Example:
 ```LIB "dmod.lib"; ring r = 0,(x,y),Dp; poly F = x^4+y^5+x*y^4; printlevel = 0; def A = Sannfs(F); setring A; poly F = imap(r,F); checkFactor(LD,F,20*s+31); // -31/20 is not a root of bs ==> 0 checkFactor(LD,F,20*s+11); // -11/20 is a root of bs ==> 1 checkFactor(LD,F,(20*s+11)^2); // the multiplicity of -11/20 is 1 ==> 0 ```