proposal
The ratio of g(y,x)/g(x,y).
proposal ratio = g(x|y)/g(y|x) = g(y,x)/g(x,y).
The ratio of the proposal function evaluated at x = current and y = proposed, where g() is some proposal function of x and y. The implementor should ensure that the returned ratio is a valid double
Return
the ratio of the proposal function
Parameters
current
the x to evaluate
proposed
the y to evaluate