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7.5.1.0. inCentralizer
Procedure from library central.lib (see central_lib).

Usage:
inCentralizer(E, S); E poly/list/ideal, S poly/ideal

Return:
integer, 1 if E is in the centralizer(S), 0 otherwise

Purpose:
check whether the elements of E are in the centralizer(S)

Example:
 
LIB "central.lib";
ring r=0,(x,y,z),dp;
matrix D[3][3]=0;
D[1,2]=-z;
nc_algebra(1,D); // the Heisenberg algebra
==> //   characteristic : 0
==> //   number of vars : 3
==> //        block   1 : ordering dp
==> //                  : names    x y z 
==> //        block   2 : ordering C
==> //   noncommutative relations: ...
poly f = x^2;
poly a = z; // 'z' is central => it lies in every centralizer!
poly b = y^2;
inCentralizer(a, f);
==> 1
inCentralizer(b, f);
==> 1
list  l = list(1, a);
inCentralizer(l, f);
==> 1
ideal I = a, b;
inCentralizer(I, f);
==> 1
printlevel = 2;
inCentralizer(a, f); // yes
==> 1
inCentralizer(b, f); // no
==> 1


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