rejectionRate calculates the fraction of time that a
Metropolis--Hastings type chain rejected a proposed move. The rejection
rate is calculates separately for each variable in the mcmc.obj
argument, irregardless of whether the variables were drawn separately or
in a block. In the latter case, the values returned should be the
same.rejectionRate(x)mcmc or mcmc.list object.== and may produce problems due
to rounding error.