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It is very easy to put a tilde over the symbol in math mode. Simply type $\tilde{a}$. But how to put a tilde under the symbol in math mode?

egreg
  • 1,121,712
Fuzzer
  • 381

5 Answers5

20

The undertilde package provides extensible tilde accents under elements in math mode via \utilde{<symbols>}. Try, for example:

\documentclass{minimal}
\usepackage{undertilde}
\begin{document}
This is $\frac{\utilde{ab}}{c} \neq \frac{ab}{c}$ and so on.
\end{document}

Alternatively, as @egreg suggests, the accents package provides \underaccent[<accent>]{<symbol>}. Try, for example:

\documentclass{minimal}
\usepackage{accents}
\begin{document}
This is $\underaccent{\tilde}{\mathcal{A}}$ and so on.
\end{document}

See page 2 of the package documentation in order to extend this using \widetilde rather than \tilde. It depends on your preference.

Werner
  • 603,163
  • 2
    It seems that \usepackage{under tilde} is unavailable in TeXLive, only in MiKTeX. – Yrogirg Jul 18 '15 at 10:30
  • 1
    The solution can be found in http://tex.stackexchange.com/questions/220626/why-is-undertilde-sty-not-found – Yrogirg Jul 18 '15 at 10:39
16

Using \underset:

\underset{\sim}{=}

...or \stackrel:

\stackrel{=}{\sim}
You
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  • 2
  • 29
  • 27
3

In 2021, the most convenient way is use the accents package

\documentclass{minimal}
\usepackage{accents}
\begin{document}
This is $\undertilde{\mathcal{A}}$ and so on.
\end{document}
Steven Sun
  • 171
2

We can define a macro:

\def\underacc #1/#2{\mathchoice{\uacc\textstyle{#1}{#2}}{\uacc\textstyle{#1}{#2}}
                     {\uacc\scriptstyle{#1}{#2}}{\uacc\scriptscriptstyle{#1}{#2}}}
\def\uacc#1#2#3{\mathop{#2{}}\limits_{#1#3{}}}

%test:
$\underacc a/\tilde, \tilde a$
wipet
  • 74,238
1

Using «amssymb» package we can use macro such as \lesssim if we want to place '~' below '<'. Similarly \eqsim and \gtrsim if we want to place '~' below = or '>'

Sagar Singh
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