newtxmath subscript spacing too large

Question

When i try to use the newtxmath package the subscript spacing is too large and looks ugly. Is there anything which can be done to rectify this. I am not talking of the "x_n" subscript spacing but the l_p subscript spacing.

Thanks

Answer 1

In math mode you can add negative spacing using \!.

\documentclass{article}
\usepackage[cmbraces]{newtxmath}
\begin{document}
Let $\{x_n\} \in l_{\!p}$
\end{document}

Answer 2

You're comparing the wrong shapes, in my opinion. Consider

\documentclass{article}
\usepackage{newtxtext,newtxmath}

\begin{document}

\makebox[1cm][r]{$x_p$}\sbox0{$_p$}%
\makebox[0pt][l]{\kern-\wd0 \smash{\vrule height 1.5ex depth 4ex width 0.1pt}}

\makebox[1cm][r]{$l_p$}

\end{document}

which typesets $x_p$ and $l_p$ so that the right borders are aligned and also draws a hairline at the left border of the subscript p (of its bounding box, to be precise).

If I change _p with _n throughout, I get

Let's try $x_n$ and $l_p$, by changing a bit the code; I see no real need for a correction.

\documentclass{article}
\usepackage{newtxtext,newtxmath}

\begin{document}

\makebox[1cm][r]{$x_n$\sbox0{$_n$}\kern-\wd0}%
\smash{\vrule height 1.5ex depth 4ex width 0.1pt}

\makebox[1cm][r]{$l_p$\sbox0{$_p$}\kern-\wd0}

\end{document}

This is your example

You see that, at high resolution, the gap is not as big as it appears at low resolution.

Here are possible corrections:

\documentclass{article}
\usepackage{newtxtext,newtxmath}

\begin{document}

Let $\{x_n\}\in l_p$

Let $\{x_n\}\in l_{\mkern-1mu p}$

Let $\{x_n\}\in l_{\mkern-2mu p}$

Let $\{x_n\}\in l_{\mkern-3mu p}$

Let $\{x_n\}\in l_{\mkern-4mu p}$

\end{document}

Seeing them in comparison makes me choose the default or the -1mu correction at most. With \! you get -3mu which is too much.