I have some code in which I write this: $\sim_r$. I want to use this command as a binary operator (in the same way as $\sim$ is normally used, but with a subscript).

I would like to create a custom command so that the subscript r appears immediately under the tilde, rather than to the right. I have tried this:


but it looks bad because there is too large a gap between the tilde and the r. Does anyone have an easy fix?

Sorry if this is too easy a question!

  • Like this: $\underset{r}{\sim}$?
    – Sigur
    Jan 20, 2020 at 14:36
  • Would your problem be solved by just placing a tilde above r? For example with $\widetilde{r}$
    – TivV
    Jan 20, 2020 at 14:39
  • tex.stackexchange.com/a/281887/197451
    – js bibra
    Jan 20, 2020 at 14:40
  • @Sigur: Thanks for your comment. I tried this, but the r floats down below the line -- it's ends up worse than $\genfrac$ unfortunately.
    – Nick Gill
    Jan 20, 2020 at 15:32
  • 1
    Are you going to use that as binary operator? So the \sim should be aligned as a\sim b, right?
    – Sigur
    Jan 20, 2020 at 15:33

2 Answers 2


The following uses \mathpalette to negotiate the different math font styles, together with \ooalign to overlay \sim and r into \simr.

enter image description here



% \reducesize{<math style>}}{<object>}
  \mathbin{% This will be a binary math symbol (in terms of spacing around it)
    \ooalign{% Overlay a number of symbols
      $#1\sim$% First symbol (\sim in correct math style)
      \cr % Move to next symbol
      \hidewidth% Move symbol to right (~\hfill)
      \raisebox% Adjust vertical positioning of <object>
        {-.25ex}% Move it down relative to current font
        {\scalebox% Change the "font size"
          {.5}% to 50% of current font size
          {$#1#2$}% <object> in current math style
        }% \raisebox
      \hidewidth% Move symbol to left (~\hfill)
    }% \ooalign
  }% \mathbin
}% \reducesize


$a \simr b_{a \simr b_{a \simr b}}$

  • Thanks heaps! I'll look into this option which seems like it will work for me.
    – Nick Gill
    Jan 21, 2020 at 13:08

Welcome to TeX.SX! Here is somewhere to get you started, and a comparison of the answers in the comments already given. I'm borrowing from another answer on how to show baselines. Let's compare a few approaches:

enter image description here

This is the code:






$a \sim b$
\hspace{5pt} $a \sim_r b$
\hspace{5pt} $a \genfrac{}{}{-2pt}{}{\sim}{r} b$
\hspace{5pt} $a \underset{r}{\sim} b$
\hspace{5pt} $a \sim_{\hspace{-7pt}r\hspace{3pt}} b$
\hspace{5pt} $a \stackengine{0pt}{\sim}{\scriptstyle{r}}{U}{\stackalignment}{\quietstack}{\useanchorwidth}{\stacktype} b$
\hspace{5pt} $a\ \stackengine{0pt}{\sim}{\scriptstyle{r}}{U}{\stackalignment}{\quietstack}{\useanchorwidth}{\stacktype}\ b$}


From your question it sounds like you want the 5th approach - simply moving the subscript in \sim_r backwards - but this is hacky, because you need to know precise symbol width to get this right (and so does not generalize). I think you actually want the 7th approach - using the stackengine package and adjusting spacing back to what it should be. There is probably a more elegant way than just putting an empty space \ in.

  • Thanks. This gives all the options very clearly, I appreciate it. I think @werner's solution and your 7th approach both give good methods for what I have in mind. Thanks again.
    – Nick Gill
    Jan 21, 2020 at 13:10

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.