Singular

7.7.20.0. coHom

Usage:

coHom(A,k); A matrix, k int

Purpose:

compute the matrix of a homomorphism Hom(R^k,A), where R is the basering. Let A be a matrix defining a map F1-->F2 of free R-modules, then the matrix of Hom(R^k,F1)-->Hom(R^k,F2) is computed.

Note:

Both A and Hom(A,R^k) are matrices for either left or right R-module homomorphisms

LIB "nchomolog.lib";
ring A=0,(x,y,z),dp;
matrix M[3][3]=1,2,3,
4,5,6,
7,8,9;
module cM = coHom(M,2);
print(cM);
==> 1,0,2,0,3,0,
==> 0,1,0,2,0,3,
==> 4,0,5,0,6,0,
==> 0,4,0,5,0,6,
==> 7,0,8,0,9,0,
==> 0,7,0,8,0,9