The map from the $i$-th cohomology of the source of $f$ to the $i$-th cohomology of the target of $f$. As an example, we map a circle into the torus in two ways, and we get two distinct maps in cohomology.
i1 : S = ZZ[x_0..x_6];
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i2 : R = ZZ[y_0..y_2];
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i3 : Torus = smallManifold(2,7,6,S);
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i4 : Circle = simplicialComplex{R_0*R_1, R_0*R_2, R_1*R_2};
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i5 : f1 = map(Torus,Circle,matrix{{S_3,S_6,S_5}});
o5 : SimplicialMap simplicialComplex | x_2x_5x_6 x_0x_5x_6 x_1x_4x_6 x_0x_4x_6 x_2x_3x_6 x_1x_3x_6 x_3x_4x_5 x_1x_4x_5 x_0x_3x_5 x_1x_2x_5 x_2x_3x_4 x_0x_2x_4 x_0x_1x_3 x_0x_1x_2 | <--- simplicialComplex | y_1y_2 y_0y_2 y_0y_1 |
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i6 : f2 = map(Torus,Circle,matrix{{S_0,S_2,S_3}});
o6 : SimplicialMap simplicialComplex | x_2x_5x_6 x_0x_5x_6 x_1x_4x_6 x_0x_4x_6 x_2x_3x_6 x_1x_3x_6 x_3x_4x_5 x_1x_4x_5 x_0x_3x_5 x_1x_2x_5 x_2x_3x_4 x_0x_2x_4 x_0x_1x_3 x_0x_1x_2 | <--- simplicialComplex | y_1y_2 y_0y_2 y_0y_1 |
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i7 : prune cohomology(1, f1)
o7 = | 1 -2 |
1 2
o7 : Matrix ZZ <-- ZZ
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i8 : prune cohomology(1, f2)
o8 = | 0 1 |
1 2
o8 : Matrix ZZ <-- ZZ
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