I want to use the double-bar notation for second-order tensors, which is common in continuum mechanics (e.g. for the strain and stress tensors).

I've searched the Comprehensive LATEX Symbol List but failed to find anything conclusive in there.

I've found this discussion, in which Stefan and Thorsten propose the alternatives below.

Is there a preferred way of typesetting this accent?

Subsidiary question: what is the difference between \bar and \Bar?

$\bar{\bar\tau} \quad
\Bar{\Bar\tau} \quad

enter image description here

  • 1
    \show\Bar gives \bar so no difference (at least in amsmath)
    – percusse
    Apr 6, 2013 at 15:08
  • amsmath.sty has \def\Bar{\bar}, so (as percusse said) there's no difference (in amsmath). Apr 6, 2013 at 15:12
  • 5
    In a previous version of amsmath, in order to get double accents one had to use the uppercase variant; this is no longer necessary from amsmath version 2. The old commands have been retained for backwards compatibility.
    – egreg
    Apr 6, 2013 at 16:53
  • There's also the Unicode combining character U+033F ◌̿ "COMBINING DOUBLE OVERLINE", which seems to introduce less vertical space between the two horizontal bars stacked: en.wikipedia.org/wiki/Overline#Unicode Jun 9, 2020 at 6:52

2 Answers 2


egreg's comment comforted me in the thought that both \bar{\bar{...}} and \overline{\overline{...}} can be used to typeset double accents without any nasty side effects.

However, the best way to replicate the double-bar notation for rank-2 tensors, as found there, for instance, seems to be using \overline{\overline{...}}.

\overline{\overline{...}} should be preferred to \bar{\bar{...}} because the \overline produces a vinculum of the same width as its argument, whereas \bar only produces a vinculum of fixed width.

$\rttensor{\epsilon} \quad \rttensor{\sigma} \quad \rttensor{G}$\\[1em]
$\rttensortwo{\epsilon} \quad \rttensortwo{\sigma} \quad \rttensortwo{G}$

enter image description here

  • Aesthetically, however, \bar\bar is more pleasing than \overline\overline.
    – JohnRos
    Oct 1, 2015 at 12:50
  • @JohnRos Not to me, especially if the tensor name is long.
    – jub0bs
    Oct 1, 2015 at 12:52

Sometimes second rank tensors are denoted with underbars, per

enter image description here

and that's


The \underbar doesn't work as well in that case.

  • this solution is inferior, though, because the variable is no longer displayed italic
    – IceFire
    Apr 10, 2019 at 9:34

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