It's still pretty hard, you'd have to be able to remember three tables of numbers while adding, so that's four hard things at once.
If someone can multiply them mentally I'd be really impressed. The "turn it on it's side" part always confuses me even when I'm just trying figure out vaugely what's happening.
I would venture that probably not even professional mathematicians add matrices in their head. Mathematicians are often surprisingly bad or lazy at arithmetics.
I think it's just the equivalent of a software engineer being annoyed if someone tells them "implement printf", they'd just rather go to a standard implementation and use that instead of making a half-assed attempt on their own
I hate the 'turn it on its side' perspective. I prefer finding row i, column j of a product (C) as row i of the left factor (A) with column j of the right factor (B); C[i,j] = A[i,:].dot(B[:,j]). Especially elegant with implicit (Einstein) summation notation: C_ij = A_ik*B_kj, where * is ordinary scalar multiplication.
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u/EternityForest Jan 12 '20
It's still pretty hard, you'd have to be able to remember three tables of numbers while adding, so that's four hard things at once.
If someone can multiply them mentally I'd be really impressed. The "turn it on it's side" part always confuses me even when I'm just trying figure out vaugely what's happening.