I have a dummy question on the calculation of the likelihood ratio in MCMC. In some codes it is written: `
$\alpha = exp(a-b)$ with $a = -\sum(obs - y_{candidate})^2$ and $b = -\sum(obs-y_{previous})^2$. I don't understand where the $exp$ comes from and why we don't calculate directly $\alpha = a/b$ ?
Thanks a lot for your help, Best, D2B