# Subscript spacing in newtxmath (comma issue)

I've found a strange behavior of newtxmath package. Using my code with documentclass[12pt]all commas are glued to the next letter, which can be hard to read:

When I changedocumentclass[11pt] everything looks very nice:

\documentclass[12pt]{report}
\usepackage[T1]{fontenc}
\usepackage{newtxmath}

\begin{document}

$$Q_i=Q_{inf,i}+Q_{vent,i}+Q_{g,c,i}$$
\end{document}


Could someone help me with this issue ?

-

The following pictures explain the problem, which should brought to the attention of the package maintainer. The comma in the math letters font (family 1) has a wrong bounding box

## With newtxmath

\documentclass[12pt]{article}
\usepackage{newtxmath}
\begin{document}
% draw a tight bounding box with hairline rules
\setlength{\fboxsep}{0pt}
\setlength{\fboxrule}{0.1pt}
\fbox{$,$}
\end{document}


## Without newtxmath

\documentclass[12pt]{article}
\begin{document}
% draw a tight bounding box with hairline rules
\setlength{\fboxsep}{0pt}
\setlength{\fboxrule}{0.1pt}
\fbox{$,$}
\end{document}


## Workaround

Use the comma from the text font

\documentclass[12pt]{report}
\usepackage[T1]{fontenc}
\usepackage{newtxtext,newtxmath}

\DeclareMathSymbol{,}{\mathpunct}{operators}{"2C}
\begin{document}

$$Q_i=Q_{inf,i}+Q_{vent,i}+Q_{g,c,i}$$
\end{document}


-
There's definitely an issue with an incorrect bounding box for the math comma of the newtxmath package. Is there maybe a secondary anomaly present as well, since the awful comma positioning happens only at 12pt but not at 11pt or 10pt? –  Mico Feb 16 '14 at 23:30
@Mico Indeed! The font used is rtxmi.pfb with the 12pt class option, but rtxmi7.pfb with the 10pt or 11pt options. The bounding box drawing was created with the 12pt option, that I forgot to add. –  egreg Feb 16 '14 at 23:38
@egreg your answer solve my problem. Thank you! In the meantime I've found another workaround. I does not repair bounding box but makes the equation looks fine, using \usepackage[libertine]{newtxmath} –  Michal Feb 17 '14 at 16:21
@MichaelSharpe have you seen this? –  Paul Gessler Mar 2 '14 at 4:35