https://en.wikipedia.org/wiki/Cracovian
The Cracovian product of two matrices, say A and B, is defined by
A ∧ B = BT A,
where BT and A are assumed compatible for the common (Cayley) type of matrix multiplication and BT is the transpose of B.
Since (AB)T = BT AT, the products (A ∧ B) ∧ C and A ∧ (B ∧ C) will generally be different; thus, Cracovian multiplication is non-associative.
A good reference how to use them and why they are useful is here (pdf):
https://archive.computerhistory.org/resources/access/text/20...
kubb•3h ago
Am I the only one for whom this crucial explanation didn’t click? Admittedly, I might be stupid.
Wikipedia is a bit more understandable: „The Cracovian product of two matrices, say A and B, is defined by A ∧ B = (B^T)A
tempodox•3h ago
tgv•3h ago
But in another link I found that it's column by column multiplication. So A × B = C, then C[i][j] = sum(A[k][i] * B[k][j]). Unfortunately, the example doesn't match that definition...
burnished•3h ago
kubb•2h ago
AdamH12113•2h ago
andrewla•2h ago
Better I think would be to say "the result in column i and row j is the sum of product of elements in column i of the left cracovian and column j of the right cracovian".
And even by this definition the example given doesn't seem to track (and the strangeness of sometimes saying "+" and sometimes not, and having both "0" and "-0" in the example is bananas!):
mci•2h ago
pomian•1h ago
pomian•1h ago
mci•2h ago