inline spacing within the `cases` command when document is in doublespace mode

Question

For journal submissions, we obviously have to use doublespace mode. But I don't want to take up even more of the page using a multi-branch cases command, which by default puts double spaces between each branch.      Obviously one can manually reduce the gap between branches with [-xpt] at the end of each branch, but it's incredibly kludgy and fragile and messes up the space between the current line and the following one.    I'm wondering if there's a package or a nice macro that would shrink the gaps in a robust way and manage the vertical height of the left brace.      Here's an MWE where the default spacing within the cases command is ridiculous.    Thanks!

documentclass{amsart}
usepackage{lipsum}
usepackage{setspace}
begin{document}
doublespacing
lipsum[1]
$x = 
begin{cases} 
a & text{if } x < -3 
b & text{if } -2 < x < 0 
c & text{if } 0 < x < 2 
d & text{if } x > 2 
end{cases}
$
lipsum[1]
end{document}

siracusa · Accepted Answer

Here's a version that redefines the cases environment to temporarily switch to single line spacing within the environment. The extra definition of new@setfontsize is only necessary to suppress a warning about setting text commands in math mode; it's otherwise the same as the original definition.

This pattern should be easily adaptable for other math environments, if necessary.

documentclass{amsart}
usepackage{lipsum}
usepackage{setspace}

makeatletter
newcommandnew@setfontsize[3]{%
    ifx protect @typeset@protect let @currsize #1fi fontsize {#2}{#3}selectfont
}
letorig@setfontsize@setfontsize
letorig@casescases
letendorig@casesendcases

renewenvironment{cases}{%
    let@setfontsizenew@setfontsize
    setstretch{setspace@singlespace}%
    letsetfontsizeorig@setfontsize
    orig@cases
}{%
    endorig@cases
}
makeatother

begin{document}
doublespacing
lipsum[1]
$x = 
begin{cases} 
a & text{if } x < -3 
b & text{if } -2 < x < 0 
c & text{if } 0 < x < 2 
d & text{if } x > 2 
end{cases}
$
lipsum[1]
end{document}

Circumscribe · Answer

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, you can add the following snippet to your preamble:
usepackage{etoolbox}
AtBeginEnvironment{cases}{renewcommandbaselinestretch{1}selectfont}

Demonstration
documentclass{amsart}
usepackage{lipsum}
usepackage{setspace}

usepackage{etoolbox} %% <- added
AtBeginEnvironment{cases}{renewcommandbaselinestretch{1}selectfont} %% <- added

begin{document}
doublespacing
lipsum[1]
$x = 
begin{cases} 
a & text{if $x < -3$} 
b & text{if $-2 < x < 0$} 
c & text{if $0 < x < 2$} 
d & text{if $x > 2$}
end{cases}
$
lipsum[1]
end{document}

Notes:

The change to baselinestretch only takes effect after selectfont is called, which is why that command is there.
Simply putting  renewcommandbaselinestretch{1}selectfont inside the cases environment doesn't work because its scope will be limited to just the first cell of the environment.

egreg · Answer

Rather than redefining cases to use singlespacing or setstretch{1}, I believe it's better to correctly set the arraystretch. Something similar should probably also be done for array, but one can use fixarraystretch{} everywhere. documentclass{amsart} usepackage{lipsum} usepackage{setspace} usepackage{xfp,etoolbox} makeatletter patchcmd{env@cases} {defarraystretch{1.2}} {fixarraystretch{1.2}} {}{} makeatother newcommand{fixarraystretch}[1]{% edefarraystretch{fpeval{#1/(baselinestretch)}}% } begin{document} doublespacing lipsum[1] $x = begin{cases} a & text{if } x < -3 b & text{if } -2 < x < 0 c & text{if } 0 < x < 2 d & text{if } x > 2 end{cases} $ lipsum[1] end{document} Just a final comment: using double spacing for submissions is a relic of the past; nowadays everybody receives PDF files and leaving space for annotations makes little sense; it just hinders reading the document on the screen.

inline spacing within the `cases` command when document is in doublespace mode

3 Answers

Demonstration

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