Index (x_i) with two rows in latex

Question

I have following problem in latex formatting:

I want to write for a matrix : $ (a_{ij})_{\underset{j=1,\ldots , n}{i=1,\ldots ,m}} $ but I want the $i=\ldots$ and $j=\ldots$ to be the same size... Does anyone know a command to do that? Thank you very much!

Answer 1

according to this https://tex.stackexchange.com/questions/80460/expression-under-summation-on-multiple-lines

$(a_{ij})_{\substack{j=1, \cdots , n \\ i=1, \cdots , m}}$

 (a_{ij})_{\substack{j=1, \cdots , n \\ i=1, \cdots , m}}