How do I do this? Say for example:
A = [a b] x [e f] x [i j]
[c d] [g h] [k l]
Or do I just multiply the first two matrices together to get a 2x2 matrix, then multiply that with the third matrix on the end?
Matrix multiplication is associative, so the above statement is unambiguous. We can either calculate
A = (XY)Z
A = X(YZ)
There is a related optimisation problem known as Matrix chain multiplication, which asks which order is the most efficient.