# source(ChainComplexMap) -- find the source of a map of chain complexes

## Synopsis

• Function: source
• Usage:
source f
• Inputs:
• Outputs:
• the source chain complex of f

## Description

In the example below, we have a map between two modules and extend it to a map between projective resolutions of the two modules. Then source gives the source of the map of chain complexes.
 i1 : R = ZZ[x,y,z]; i2 : M = R^1/(x,y,z); i3 : N = R^1/(x^2,y^2,x*y*z,z^2); i4 : g = map(N,M,x*y); o4 : Matrix i5 : f = res g; i6 : source f 1 3 3 1 o6 = R <-- R <-- R <-- R <-- 0 0 1 2 3 4 o6 : ChainComplex
(That was an expensive way of resolving M.)