sigma0 in MCMCController and OptimisationController mean different things

[chonlei]

I know we'd run out of symbols at some point, but the sigma0s in MCMCController and OptimisationController mean subtly different things, one is covariance matrix $\Sigma$ and the other is standard deviation $\sigma$.

Would it be better to call the covariance matrix cov0, C0 or something? Or simply capitalise Sigma0 in the MCMCController to distinguish the two?!