For the two matrices A and B, (AB)i,j = ri . dj ---- . refers to dot product ---- ri is the ith row in A and dj is the jth column in B. Let us say that A and B are n x n system of column vectors. Then a row vector ri of A would correlate to a component vector of the sum of the column vectors in A specified by the ith space. Wouldn't that imply that ri . dj would only be the product between the element dj,i and the sum of the elements of ri or am I just being too technical?