# How to control the alignment of the brace in a dcases environment

The following code

$$\begin{dcases} u = \frac{\sqrt{2}}{2}(i+j)\\ v = k \end{dcases}$$

results in the following display

that I find particularly disgraceful. Is there a way to lower the brace to make it look more like this

?

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You can "smash" the fraction from the top using \smash[t]. Like this:

\documentclass{article}
\usepackage{mathtools}
\begin{document}

$$\begin{dcases} u = \smash[t]{\frac{\sqrt{2}}{2}(i+j)}\\ v = k \end{dcases}$$

\end{document}

The command \smash[b] would be useful for the last line.

Workaround: since I don't suppose you need it regularly, a manual tweak suggested by egreg is possible. Here, we increase the vertical space above the equation, and by grouping we ensure that the effect will be local.

\begingroup\addtolength{\abovedisplayskip}{4pt}$$\begin{dcases} u = \smash[t]{\frac{\sqrt{2}}{2}}(i+j)\\ v = k \end{dcases}$$\endgroup
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Works like a charm. Thanks a lot. – Evpok Dec 9 '12 at 21:04
This has some small inconveniences: the vertical placement of the equation will not take into account the smashed fraction, so it can end too near the preceding line. – egreg Dec 9 '12 at 21:04
@egreg Actually, the [t] option only smashes the top part, so there is no such issue. – Evpok Dec 9 '12 at 21:12
@Evpok The issue is there: the square root is placed too near the line preceding the display, for my tastes. – egreg Dec 9 '12 at 21:22
@egreg Oh, sorry, I misread your comment. Reader from the future: the aforementionned chat is at chat.stackexchange.com/transcript/message/7199794#7199794 – Evpok Dec 9 '12 at 21:59