Correct mathematical expression

Question

I am a biologist. My apologies if I my question is too basic.

I am writing a scientific manuscript and I would like to express the following with a correct mathematical expression: for a list of numbers (from $x_1$ to $x_n$) calculate the product of $x_1$ to $x_n$ every time $x$ is above $0$.

Thanks a lot for the help.

Answer 1

You probably look for $$ \prod_{\substack{1\leq j\leq n \\x_j>0}} x_j, $$ where I assume that $x$ above $0$ means $x_j>0$ (you did not define $x$).