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My Jacobian matrix evaluated at the equilibrium is denoted by J_E. I typed for its trace as

tr\textit{J_E}.

And the result is very strange. tr appears good but \textit{J_E} part is unlimitedly repeated with its size gradually decreasing.

It looks something like:

Like this

where the J_E part is gradually getting smaller.

What is happening here?

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  • 1
    Welcome to TeX.SE. Not sure what is going on as you did not post a full MWE the reproduces the problem. But you should be using \usepackage{amsmath}\DeclareMathOperator{\trace}{tr} in the preamble and then $\trace J_E $. The underscore to indicate subscript has to be in math mode. Oct 6 '14 at 3:26
  • Could you add a picture, showing this strange result? Now you have enough reputation to do it... Oct 6 '14 at 3:30
  • @Peter Grill thanks so much. My problem is resolved!
    – ppp
    Oct 6 '14 at 3:49
  • 2
    I think your editor is compiling in nonstop mode and it keeps trying to add the missing $ sign since inside \textit an underscore should be in math mode.
    – percusse
    Oct 6 '14 at 5:23
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Why should you type \textit{J_E}? This is wrong for several reasons.

  1. _ requires math mode and the argument to \textit is typeset in text mode (as the command name suggests).

  2. \textit is the wrong command for typesetting a math variable: math mode should be used.

  3. You're right that “tr” for the trace should be in upright type, but typesetting a formula not in math mode just for this is misusing the tool.

\documentclass{article}
\usepackage{amsmath}

\DeclareMathOperator{\tr}{tr}

\begin{document}
$\tr J_{E}$ is the trace of $J_{E}$.
\end{document}

Now, why the four repetitions? You first of all get an error message that says

! Missing $ inserted.
<inserted text> 
                $
l.8 \textit{J_E}

(the line number can be different, of course). After this the output is unpredictable, because when TeX discovers the error it's too late for doing a sensible fix.

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