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7.5.20.0. isCentral
Procedure from library nctools.lib (see nctools_lib).

Usage:
isCentral(p); p poly

Return:
int, 1 if p commutes with all variables and 0 otherwise

Purpose:
check whether p is central in a basering (that is, commutes with every generator of the ring)

Note:
if printlevel > 0, the procedure displays intermediate information (by default, printlevel=0 )

Example:
 
LIB "nctools.lib";
ring r=0,(x,y,z),dp;
matrix D[3][3]=0;
D[1,2]=-z;
D[1,3]=2*x;
D[2,3]=-2*y;
def S = nc_algebra(1,D); setring S;
S; // this is U(sl_2)
==> // coefficients: QQ
==> // number of vars : 3
==> //        block   1 : ordering dp
==> //                  : names    x y z
==> //        block   2 : ordering C
==> // noncommutative relations:
==> //    yx=xy-z
==> //    zx=xz+2x
==> //    zy=yz-2y
poly c = 4*x*y+z^2-2*z;
printlevel = 0;
isCentral(c);
==> 1
poly h = x*c;
printlevel = 1;
isCentral(h);
==> Non-central at: y
==> Non-central at: z
==> 0


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