Here is e^{-\lvert\frac{x-\mu}{\sigma}\rvert}: $e^{-\lvert\frac{x-\mu}{\sigma}\rvert}$

The bars on the absolute value are too small, so I decided to make them bigger. Using \left and \right made them look pretty good:

e^{-\left\lvert\frac{x-\mu}{\sigma}\right\rvert}: $e^{-\left\lvert\frac{x-\mu}{\sigma}\right\rvert}$

But I thought I'd see what happened if I used \bigl and \bigr, which are supposed to increase the size of the delimiters by one quantum. And I found that the bars became much too big and fat:

e^{-\bigl\lvert\frac{x-\mu}{\sigma}\bigr\rvert}: $e^{-\bigl\lvert\frac{x-\mu}{\sigma}\bigr\rvert}$

I thought that \bigl and \bigr produced the smallest possible bigger-than-normal delimiters, and so \left and \right delimiters would necessarily be at least as big.

Is the bug in my understanding of \bigl and \bigr, or in their implementation?

I am using:

Google Chrome 23.0.1271.64 (Official Build 165188)
WebKit 537.11 (@132838)
JavaScript V8

Here's a screenshot:



  1. With a different computer, the \bigl/\bigr bars don't look absurdly thick, although they are still taller than the \left/\right bars:

Google Chrome 18.0.1025.142 (Official Build 129054)
OS Linux
WebKit 535.19 (@111933)
JavaScript V8

Addendum 2022-11-11

The bars produced by \bigl and \bigr are still fatter on Chrome than they ought to be:

Chrome 107.0.5304.87 screenshot

This is:

Chrome: 107.0.5304.87 (Official Build) (x86_64) 
OS: macOS Version 12.6 (Build 21G115)
WebKit: 537.36
JavaScript: V8

2 Answers 2


There are actually two factors involved here. Mythealias has already discussed the TeX language issue of the way that \left...\right work in comparison to \bigl and \bigr, which explains the difference in height. MJD also complains about the thickness of the characters, which is actually a MathJax rendering issue, not a TeX one.

It turns out that the characters used for the vertical bar for \left...\right are taken from the script-sized font, while the ones for \bigl and \bigr are taken from the normal sized font. That means that the latter are heavier looking as they are slightly thicker. Also, the vertical bars are formed by using multiple smaller vertical bars, and they are overlapped in order to get the right total height. In this case, the original characters are nearly tall enough by themselves, but not quite, so two fairly large character are overlapping. That causes the anti-aliasing to appear extra heavy in the overlap area. So there are two reasons for the excessive thickness of the \big versions in this case.

I don't recall the reason why the script size wasn't used in this case, and I suspect it is not necessary. I will open an issue tracker for it so that it is taken care of in the next release of MathJax.

  • $\begingroup$ Thanks; this is exactly the response I was hoping to get. $\endgroup$
    – MJD
    Commented Nov 12, 2012 at 22:04
  • $\begingroup$ What's the best place to report MathJax formatting and layout problems? se.math seems like a strange place to do it, but it does provide a lot of useful infrastructure for attaching screenshots and the like. What is most convenient for you? $\endgroup$
    – MJD
    Commented Nov 15, 2012 at 15:21
  • 1
    $\begingroup$ Meta for se.math is fine (I check that regularly), but perhaps the best place is the MathJax User's Forum which is a Google group. Not quite as flexible an infrastructure, but it is where the MathJax users are linked in. $\endgroup$ Commented Nov 16, 2012 at 17:09
  • 1
    $\begingroup$ Was this taken care of in a later release of MathJax? It still seems to be behaving in the way I described. $\endgroup$
    – MJD
    Commented Nov 11, 2022 at 14:42
  • 4
    $\begingroup$ @MJD, it was fixed in v3, but StackExchange is still using version 2.7.5 (not even the latest v2, which is 2.7.9). Version 4.0 is currently in alpha release, and it includes the automatic line-breaking that was missing from v3, so perhaps StackExchange will consider updating to v4.0 when its production release is made (early 2023, I hope). $\endgroup$ Commented Nov 11, 2022 at 19:09
  • $\begingroup$ Thanks for your timely reply! $\endgroup$
    – MJD
    Commented Nov 11, 2022 at 19:12

I don't think it is a bug. \left and \right constructs account for the size of content between them, whereas \bigl and \bigr are of predefined size. The l and r are to account for horizontal spacing. See here.

I think this question is better suited for tex.SE.

This is the output from latex with and without exponentiation (which uses scriptsize to change font size).

enter image description here


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