# Two lines subscript in summation symbol - LaTeX

$\sum_{ \substack{ n \in \Lambda \\ 0 \lt i \lt n } } f_{n} (a_{i})$


$\sum_{ \substack{ n \in \Lambda \\ 0 \lt i \lt n } } f_{n} (a_{i})$

If the text under the sum symbol is too long, the spacing around the sum symbol increases and the equation may look bad.

$\sum_{ \substack{ n \in \Lambda \\ 0 \lt i \lt \frac{\sqrt{n}}{2} + \sin n + n^{2p} } } f_{n} (a_{i})  \[ \sum_{ \substack{ n \in \Lambda \\ 0 \lt i \lt \frac{\sqrt{n}}{2} + \sin n + n^{2p} } } f_{n} (a_{i})$

The command mathclap fixes it.

$\sum_{ \mathclap{ \substack{ n \in \Lambda \\ 0 \lt i \lt \frac{\sqrt{n}}{2} + \sin n + n^{2p} } } } f_{n} (a_{i})$


$\sum_{ \mathclap{ \substack{ n \in \Lambda \\ 0 \lt i \lt \frac{\sqrt{n}}{2} + \sin n + n^{2p} } } } f_{n} (a_{i})$