Ahhhhh, I get it. I was thinking HxW for some reason. Bleh. Linear algebra is like the brain scrambling olympics sometimes.
So the MxN * NxP rule means you'll always have a workable number of rows and columns. Okay.
Okay, lemme write this out...
[a, b, c] [j, k] [d, e, f] * [l, m] [g, h, i] [n, o]
Okay, so that would be invalid because it's 3x3 * 2x3?
We did one where we multiplied a 3x3 by a 1x3(vector, though he didn't call it that). Is that just considered a different case since the vector can be used for each row?
Edit - Bzzzzzzzzzt. I got it. -.-
It would be
[aj+bl+cn, ak+bm+co] [dj+el+fn, dk+em+fo] [gj+hl+in, gk+hm+io]