<p>I tried writing $\hat{C}_{t-1}$ in my (possibly off-topic?) question here:
<a href="https://stats.stackexchange.com/questions/1095/">Tonga: low rank approximation of the natural gradient, question regarding Le Roux et al. 2007</a>
but the \hat seems to mess with the correct processing of the rest of the question, so I had to remove that hat. But hats work in the other formulas, wonder what is going on here? 
Also would be nice if writing matries using \array would be supported...</p>
