General interpretation
When given a summation as below, what is the comen interpretation when no more details are given apart from j,m being part of the positive integers.
Are we given $(j,m)$, taking the sum $(1,1),(1,2),(1,n),(2,1),(n,1)....$ (all possible combinations) or are we using the sum where (j,m) goes from $(1,1),(2,2),....(n,n)$
How does the index go?
$\sum _{j,m}u_{j}c_{j,m}U_{m}$
All possible combinations.
If $u$ is a column vector $c$ is a matrix and $U$ is a column vector, the expression is equvalent to the matrix multiplication$$u^TcU$$