I have an array inside an equation in a beamer presentation. I tried scaling it down using `resizebox`

but it gives me error :

```
\begin{equation}
\label{eq:recursive}
\resizebox{\linewidth}{!}{
R_{k+1}(a,b) =
\left\{ \begin{array}{rl}
1 & \mbox{if } a=b \\
0 & \mbox{if } I(a)=\phi \mbox{ or } I(b)=\phi \\
\frac{C}{|I(a)||I(b)|}\sum_{i=1}^{|I(a)|}\sum_{j=1}^{|I(b)|} R_k(I_i(a),I_j(b)) & \mbox{otherwise } \\
\end{array}\right.
}
\end{equation}
```

any suggestions?

## Best Answer

If you really need numbering, you can do like

Note that I used

`dcases`

provided by`mathtools`

, which gains some horizontal space as the limits are typeset above and below the summation sign. Alternatively, you can typeThis will use smaller summation signs.

Notes.The

`cases`

(or`dcases`

) environment is more convenient than using`array`

.For the conditions, it's better to use

`\text`

and switch to math mode inside it, rather than using clumsy`\mbox`

commands with spaces.