function [px] = gammapdf(x,alpha,beta,logoption)%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%   [px] = gammapdf (x,alpha,beta,logoption)%%   computes Gamma propability density for x  given%   scale matrix parameter beta and shape parameter alpha%%               alpha%         |beta|         alpha-1%   p(x)= ------------- x        exp (-beta x)%         Gamma (alpha)%              %%%   if logoption is set to one, the log-propability is returned%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%if nargin<4,  logoption=0;end;if alpha<=0,   error('alpha must be positive');end;if beta<=0,   error('beta must be positive');end;if any(x<=0),   error('Density only defined for positive x');end;x=x(:);N=length(x);normconst=alpha*log(beta)-gammaln(alpha);px=zeros(N,1);px = (alpha-1)*log(x) - beta*x;if logoption  px=px+normconst;else  px=exp(px+normconst);end;