Writing mod in congruence problems without leading space

Question

I have been writing

$a \equiv r (\mod n)$

but this puts a space between the ( and mod. For example, r ( mod n ) instead of r (mod n). So, how do you write r (\mod n) without that space? What would be the correct way to write $a \equiv r (\mod n)$ ?

You should use \pmod (from amsmath), perhaps utilizing the redefinition as in Removing extra space with \pmod command. — Werner, Oct 09 '13 at 05:45
and if one drops parentheses, \bmod also from amsmath is an option. — , Oct 10 '13 at 15:36

Werner · Answer 1 · 2017-03-09T16:17:01.043

115

The spacing issue is an obvious indication that it's not meant to be used that way. However, you could wing your own, depending on the sophistication you're after:

enter image description here

\documentclass{article}

\usepackage{amsmath}
\newcommand{\Mod}[1]{\ (\mathrm{mod}\ #1)}

\begin{document}

\begin{align*}
  a &\equiv r \mod n \\
  a &\equiv r \pmod{n} \\
  a &\equiv r \Mod{n}
\end{align*}

\end{document}

edited Mar 09 '17 at 16:17

answered Oct 09 '13 at 05:59

Werner

603,163

1

This is great! I like how \Mod{n} looks. The only problem I'm encountering with \Mod{n} is that the "mod" becomes italicized in theorem/lemma/example/proof/etc. environments. – EthanAlvaree Aug 31 '14 at 19:12
1

@Mathemanic: You can try using \textup (or perhaps \mbox) instead of \text. – Werner Aug 31 '14 at 19:38
4

This should be \mathrm{mod}. – egreg Mar 09 '17 at 13:23
1

@egreg why is it \mathrm over \operatorname? – It'sNotALie. Nov 03 '19 at 22:59
1

@It'sNotALie. Because this is not an operator. – egreg Nov 03 '19 at 23:27
What is the obvious way that it is supposed to be used? – copper.hat Nov 21 '21 at 04:33

score 38 · Answer 2 · answered Apr 06 '14 at 14:33

38

I think $a \equiv r \;(\bmod\; n)$ does what you want (as mentioned by jfbu in the comment).

answered Apr 06 '14 at 14:33

craastad

501

score 11 · Answer 3 · answered Mar 09 '17 at 13:19

Both the latex kernel and amsmath provide the command \pmod. In the latex kernel \pmod provides a fixed amount of space before (mod ...). The amsmath version is slightly more sophisticated, using a smaller amount of space when not in a display. So one way is to define a new command that temporarily switches off the display mode:

\usepackage{amsmath}

\makeatletter
\newcommand{\tpmod}[1]{{\@displayfalse\pmod{#1}}}
\makeatother

\documentclass{article}

\usepackage{amsmath}

\makeatletter
\newcommand{\tpmod}[1]{{\@displayfalse\pmod{#1}}}
\makeatother

\begin{document}

Text (no change): \( a\tpmod{b} \) vs.\ \( c\pmod{d} \).

Display:
\begin{gather*}
  a\tpmod{b} \\
  \intertext{vs.}
  c\pmod{d}.
\end{gather*}

\end{document}

score 4 · Answer 4 · edited Jun 20 '21 at 20:09

4

This issue can easily be handled by using \pmod.

edited Jun 20 '21 at 20:09

Mensch

65,388

answered Jun 20 '21 at 19:45

F. A. Mala

229

Writing mod in congruence problems without leading space

4 Answers4

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