- #1

- 41

- 1

[tex]

\sum_{i,j=1}^n A_{i,j}

[/tex]

Where A is an (n x n) matrix. I am a little unsure of what the summation is

*over*, due to the odd notation "i,j = 1". My first guess is that this is shorthand for

[tex]

\sum_{i=1}^n \sum_{j=1}^n A_{i,j}

[/tex]

But I am wondering if it could also mean the sum over the diagonal elements of the matrix, i.e.:

[tex]

\sum_{i=1}^n A_{i,i}

[/tex]

I am guessing it is the first, but I want to make absolutely sure.