what should I do to stop the cases environment compressing the first line of the following?

\alpha_{mn} = \begin{cases} \frac{16\mu^2}{mn\pi^2\left[\pi^2(m^2/a^2 + n^2/b^2) - \mu^2\right]} &\mbox{for } m \mbox{ and } n \mbox{ odd;} 
\\ 0 &\mbox{for } m \mbox{ or } n \mbox{ even;} \end{cases} \\[1ex]

I'm not sure to do tex on this site, but if anyone tries it they see the first case is compressed because it's a fraction.

  • 2
    Use \dfrac for \displaystyle\frac Commented Apr 21, 2014 at 19:23
  • 1
    Yes, cases uses \textstyle; the package mathtools provides dcases.
    – egreg
    Commented Apr 21, 2014 at 19:23

2 Answers 2


The package mathtools (that also loads amsmath) provides dcases and dcases*:

\alpha_{mn} =
\frac{16\mu^2}{mn\pi^2[\pi^2(m^2/a^2 + n^2/b^2) - \mu^2]} &
  for $m$ and $n$ odd;\\
0\vphantom{\frac{0}{0}} & for $m$ or $n$ even;

enter image description here

The difference between cases and dcases is that display style is used in the latter, but not in the former. The dcases* form sets the second part in text mode, making it more convenient to type textual conditions.

The \vphantom{\frac{0}{0}} is an adjustment to make the construction more balanced. Note that you don't need \left and \right in the denominator, which would make the brackets too big.


Two alternatives (I couldn't use the mathtools package because it was marked as obsolete) which work in the cases environment:

  1. use the function \mathlarger{} including the fraction you want to be displayed larger (also works with \sum symbol)

  2. (only for fractions) use the function \dfrac{} instead of \frac{}

  • 3
    Welcome to TeX.SX. mathtools is not an obsolete package, so I wonder why you'd get that message. And amsmath is required for \dfrac, isn't it? Commented Sep 4, 2014 at 13:54
  • Thank you! I'm not sure why mathtools is marked as obsolete, the software wouldn't let me install it as other packages. These are my first 72 hours using LaTeX so I can't provide more info.. And to complete the discussion the package relsize is required for \mathlarger{}.
    – user61877
    Commented Sep 4, 2014 at 16:59
  • Which TeX distribution do you use? It's very odd that you would get a message that the mathtools package is obsolete; that's definitely not the case. Incidentally, the \dfrac macro was mentioned in a comment below the original posting.
    – Mico
    Commented Sep 4, 2014 at 17:42
  • mathtools and friends have recently been ”rearranged“ ... i wonder if that's what is being referenced? (i catalogued the change on 20 aug) Commented Sep 4, 2014 at 20:35
  • my version is TeXstudio 2.8.2
    – user61877
    Commented Sep 5, 2014 at 7:10

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