Yo,
I need some help with understanding matrix multiplication by columns. Consider the two matrices:
$\left( \begin{array}{ccc} 1 & 2 & 3 \\ 6 & 5 & 4 \\ 7 & 8 & 9 \end{array} \right) \left( \begin{array}{ccc} 3 & 2 & 1 \\ 4 & 5 & 6 \\ 9 & 8 & 7 \end{array} \right) $
So I'm familiar with the standard algorithm where element $AB_{ij}$ is found by multiplying the $i^{th}$ row of A with the $j^{th}$ column of B.
Apparently there is another way to multiply matrices where you work with whole columns of A to get the product AB. Does anyone know how to do that? If so, could you please provide a general algorithm? I've never heard of it and I can't find it anywhere.