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I am facing a problem in some of my equations written in latex as it is distributed over two lines and I don't why this happens. For example, the attached picture shows the script and the output in the pdf files. Any help will be highly appreciated.

This is the script of defining the function

This is the output in the pdf file

Furthermore, after the bracket some words like (u) is not written at all. Why is that. Thanks in advance.

frabjous
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Medo2018
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    Please never post screenshots of code. Don't make others retype your code. Post a complete minimal document in a code block that can be copied and pasted and run as is. That code has errors. Never ignore errors. What are you trying to accomplish with \emph in math mode? Math mode letters are italicized by default. Does \sigma_i = \upsilon_p \rho (\dot{u}^{ff} - \dot{u}_{i}^{m}) do what you want? If not, post a minimal working example. – frabjous Jun 25 '22 at 14:49
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    Welcome to tex.sx. There should be error messages in your log pointing out the problems. The main one is that equation establishes math mode, and using $ within display math is incorrect -- it turns off math mode and changes many processing conventions (also causing many additional irrelevant error messages). Also, \emph shouldn't be used within math mode; letters within math are by default italic. – barbara beeton Jun 25 '22 at 14:52
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    never ignore error messages, after any error, if you scroll past and make a pdf it is just usable as a debugging aid, tex makes no attempt at making usable output it just tries to recover enough to process the rest of th file, for checking. – David Carlisle Jun 25 '22 at 16:39

1 Answers1

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Please, consult a beginner's manual for LaTeX. See What are good learning resources for a LaTeX beginner?

You mustn't use $ inside equation and that's the reason for the errors you get: equation already uses math mode.

Also, \emph is not for math formulas; single letters will be automatically typeset in italics.

\documentclass{article}
\usepackage{amsmath}

\begin{document}


\begin{equation}\label{NEW}
\sigma_{i} = \upsilon_{p}\rho(\dot{u}^{ff}-\dot{u}_{i}^{m})
\end{equation}


\end{document}

enter image description here

If ff is to be a single symbol, you might use \mathit{ff}

\documentclass{article}
\usepackage{amsmath}

\begin{document}


\begin{equation}\label{NEW}
\sigma_{i} = \upsilon_{p}\rho(\dot{u}^{\mathit{ff}}-\dot{u}_{i}^{m})
\end{equation}


\end{document}

enter image description here

egreg
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