In the following image there are two different styles used for matrix index l. The first one is the default one. How can one get the second one?

The code is for the first equation is
$\sum_{kl}V_{ki}V_{lj}A_{kl}$
In the following image there are two different styles used for matrix index l. The first one is the default one. How can one get the second one?

The code is for the first equation is
$\sum_{kl}V_{ki}V_{lj}A_{kl}$
(Turning comment into answer)
The symbol is called \ell, but I would recommend not using it, at least in that context where a normal l (italic ell) is not subject to confusion. On older typescripts it was difficult to distinguish between l (italic ell) and 1 (one), so many took the habit of using a different letterform for l (italic ell).
$\sum_{k\ell}V_{ki}V_{\ell j}A_{k\ell}$
\ell, but I would recommend not using it, at least in that context where a normal "l" is not subject to confusion. On older typescripts it was difficult to distinguish between "l" and "1", so many took the habit of using a different letterform for "l". – egreg Jan 27 '12 at 16:48\ellas egreg suggests and 2) removing all\rm{...}from your code and removing\,from the end:$\sum_{k\ell}V_{ki}V_{\ell j}A_{k\ell}.$– yo' Jan 27 '12 at 16:52$\ell$over$l$, I really want to avoid the confusion, especially when half of the digits in the manuscript are1. – yo' Jan 27 '12 at 16:53\ellshould not be necessary at all. – egreg Jan 27 '12 at 16:58\ellis the difference I was searching for, thanks egreg. – liberias Jan 27 '12 at 17:01