How to force the subscript stay under summation/product?

Post date: Aug 31, 2011 1:43:07 PM

Normally, when you use

\[ A=\sum_{i\in S} a_i \],

there might be some chances that the subscript will be put horizontally on the right hand of the summation which make the equation too long. We can force the subscript to stay under the summation by adding \limits right after \sum:

\[ A=\sum\limits_{i\in S} a_i \]