User-defined matrix operation

hi all, I am a little bit confused. I simplified a big problem into this:
A(k,l)%B(m,n)*C(i,j)
can anyone explain is it matrix A that is being multiplied or matrix B, thanks

The expression multiplies an element of B by an element of C. As B is a member of a two-dimensional array A, the actual matrix B that is used depends on the indices in A, but that is it.