DGAMMA

dgamma
The gamma density function

         f = dgamma(x,a)
	Input	x	real
		a	positive real
		(x,a can be vector or matrix with common dimensions)

	Output	f	gamma density function with parameter a 
			at the values of x : 
			f(x)=x.^(a-1)exp(-x)./Gamma(a)1_{x>=0}