Minimal implementation of matrix multiplication

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I had a need for basic matrix multiplication for a CeTZ diagram, so:

#let matvec(A, v) = A.map(Ai => Ai.zip(v).map(array.product).sum())
#let transpose(A) = range(A.first().len()).map(j => A.map(Ai => Ai.at(j)))
#let vecmat(v, A) = matvec(transpose(A), v)
#let matmat(A, B) = A.map(Ai => vecmat(Ai, B))

// Tests
#assert(matvec(((1, 2), (3, 4)), (2, 3)) == (8, 18))
#assert(transpose(((1, 2), (3, 4), (5, 6))) == ((1, 3, 5), (2, 4, 6)))
#assert(vecmat((2, 3), ((1, 2), (3, 4))) == (11, 16))
#let A = ((1, 2), (3, 4))
#let B = ((1, 3, 4), (2, 1, 8))
#import "@preview/cetz:0.3.2": util.matrix
#assert(matmat(A, B) == matrix.mul-mat(A, B))

Maybe it will be useful to someone else… As you can see with the last test, I then realized I could just use the CeTZ util functions instead :sweat_smile: But sometimes it might make sense to avoid that dependency.

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Hi, thanks for your post! It helps me to improve my knowledge about Typst. How did you know about matrix.mult-mat(A,B)? I have been using CeTZ and I haven’t realized it until now. I searched it and couldn’t find it :astonished:.

On the other hand, I copy-paste your code with #assert(matmat(A, B) == matrix.mul-mat(A, B), message: “Hi”), but nothing happens :thinking:

3

Hi @SilverWolf, welcome to the forum :slight_smile:

I found matrix.mult-mat by going through the CeTZ source code, but it is actually documented here: Matrix | CeTZ Documentation

The assert is supposed to output nothing: it checks that the expression inside is true. This is used to test that the code works as expected and to generate a compilation error if not.