to the model initially,
otherwise a flat prior is assumed.  The <tt>MCMCCalculator</tt> returns an <tt>MCMCInterval</tt>, which produces
the smallest interval by taking a contour of the posterior.  This first version only supports
1,2, and 3 dimensional intervals, but will be generalized in the next release.
</p>
<p>
In addition to the MCMC implementation in RooStats, one can export their model and dataset into a workspace,
 and then use the Bayesian Analysis Toolkit (BAT) for the MCMC.  There is a wrapper 