Problem with \doublespacing and cases - TeX

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You can accomplish this by setting `\baselinestretch` back to `1` inside the definition of the `cases` environment. This is a multiplier for the distance between lines in a paragraph (and also between the rows of the `cases` environment) and it was set to `1.667` by `\doublespacing`.

To patch `cases`, add any one of the following three snippets to your preamble (whichever you prefer):


```
\usepackage{etoolbox}
\AtBeginEnvironment{cases}{\renewcommand\baselinestretch{1}\selectfont}
```

```
\let\originalcases\cases
\renewcommand\cases{%
  \renewcommand\baselinestretch{1}\selectfont
  \originalcases
}
```

```
\edef\cases{%
  \unexpanded{\renewcommand\baselinestretch{1}\selectfont}%
  \unexpanded\expandafter{\cases}%
}
```

Note: 
* The change to `\baselinestretch` only takes effect after `\selectfont` is called, which is why that command is there.
* Simply putting  `\renewcommand\baselinestretch{1}\selectfont` inside the `cases` environment doesn't work because its scope will be limited to just the first cell of the environment.
* Putting `\renewcommand\baselinestretch{1}\selectfont` in the equation itself (or changing `\everydisplay` to put it in every display equation) won't affect the spacing around the the first equation, but it will reduce the skip above (but not below) the second equation. The spacing around the first is unaffected because it has a very tall line (due to the cases) that is already placed more than the stretched `\baselineskip` below the previous baseline. (So don't do this.)

### Demonstration

```
\documentclass{book}
\usepackage{setspace}

\usepackage{mathtools}
\usepackage{physics}
\usepackage{amssymb}
\newcommand{\punc}[1]{\,\text{#1}}

\usepackage{etoolbox} %% <- added
\AtBeginEnvironment{cases}{\renewcommand\baselinestretch{1}\selectfont} %% <- added

\begin{document}
\doublespacing
Something before Something before Something before Something before Something before Something before Something before Something before 
\[ %% <- \setstretch{1} removed
L_i =\begin{cases}
1\text{,}&\text{when }X_i \leq \xi_i\text{, with probability } p\\
0\text{,}&\text{otherwise, with probability } 1-p\punc{.}
\end{cases}
\]
something after something after something after something after something after
\[x+y=z
\]
something after something after something after something after something after
\end{document}
```

![casesspace.png](/image?hash=daae31920d2944c6d42c1151ba18e4b94a9feb11066424d6e6fea2b0b1ff2bda)

N.B. Putting that in the first equation without braces does produce the same spacing for the first equation, but that's only because `\baselineskip` isn't used for that equation because the `cases` environment makes the line in that equation very tall. The spacing around the second equation would be affected by doing this.

You can use `\renewcommand\baselinestretch{1}\selectfont` instead of `setstretch{1}`. The effect on the spacing within `cases` is the same, but this doesn't do most of the unnecessary things egreg talked about and doesn't lead to a warning. (I updated my answer to reflect this new insight.)

I haven't read the original question, but would appreciate it if someone could try a really simple hack -- just wrap the full `\[ ... \]` in braces to isolate the local `\setstretch`. (I can't test it because I don't have a local TeX installation, use the one at my usual "remote location", but that can't be reached at the moment. Oh, new computer blues!)

I should've actually read the answer linked to by samcarter before posting mine. It looked unnecessarily nasty because it starts by redefining `\@setfontsize`, but I I now see that it does exactly the same thing and the nastiness is only there to suppress a warning that is not suppressed in my answer.

Would https://tex.stackexchange.com/a/343148/36296 give enough space? ``` \documentclass{book} \usepackage{setspace} \usepackage{mathtools} \usepackage{physics} \usepackage{amssymb} \newcommand{\punc}[1]{\,\text{#1}} \makeatletter \newcommand\new@setfontsize[3]{% \ifx \protect \@typeset@protect \let \@currsize #1\fi \fontsize {#2}{#3}\selectfont } \let\orig@setfontsize\@setfontsize \let\orig@cases\cases \let\endorig@cases\endcases \renewenvironment{cases}{% \let\@setfontsize\new@setfontsize \setstretch{\setspace@singlespace}% \let\setfontsize\orig@setfontsize \orig@cases }{% \endorig@cases } \makeatother \begin{document} \doublespacing Something before Something before Something before Something before Something before Something before Something before Something before \[ %\setstretch{1} L_i =\begin{cases} 1\text{,}&\text{when }X_i \leq \xi_i\text{, with probability } p\\[.5\baselineskip] 0\text{,}&\text{otherwise, with probability } 1-p\punc{.} \end{cases} \] something after something after something after something after something after \[x+y=z \] something after something after something after something after something after \end{document} ```

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