PGAMMA

pgamma

The gamma cumulative distribution function

         F = pgamma(x,a)
	Input	x	real
		a	positive real, parameter of the gamma distribution
		(x and a can be matrix with common size)

	Output	F	F =Prob(X<x) where X is a random variable with a gamma
			distribution of parameter a
	( the gamma density function with parameter a is :
	   x --> x.^(a-1)exp(-x)./Gamma(a)1_{x>=0} )