class RooStats::PdfProposal: public RooStats::ProposalFunction

 Populate xPrime with a new proposed point

 Determine whether or not the proposal density is symmetric for
 points x1 and x2 - that is, whether the probabilty of reaching x2
 from x1 is equal to the probability of reaching x1 from x2

 Return the probability of proposing the point x1 given the starting
 point x2

 Set the PDF to be the proposal density function

 Get the PDF is the proposal density function

 specify a mapping between a parameter of the proposal function and
 a parameter of interest.  this mapping is used to set the value of
 proposalParam equal to the value of update to determine the
 proposal function.
 proposalParam is a parameter of the proposal function that must
 be set to the value of update (from the current point) in order to
 propose a new point.

 Set how many points to generate each time we propose from a new point
 Default (and minimum) is 1

 set whether we own the PDF that serves as the proposal density function
 By default, when constructed, PdfProposal does NOT own the PDF.

virtual void SetIsAlwaysSymmetric(Bool_t isAlwaysSymmetric)
{ fIsAlwaysSymmetric = isAlwaysSymmetric; }

Bool_t fIsAlwaysSymmetric; // does Q(x1 | x2) == Q(x2 | x1) for all x1, x2
 determine whether these two RooArgSets represent the same point