function p = dirichletpdf(x, alpha)%DIRICHLETPDF Dirichlet probability density function.%   p = dirichletpdf(x, alpha) returns the probability of vector%   x under the Dirichlet distribution with parameter vector%   alpha.%%   Author: David Ross%-------------------------------------------------% Check the input%-------------------------------------------------error(nargchk(2,2,nargin));% enusre alpha is a vectorif min(size(alpha)) ~= 1 | ndims(alpha) > 2 | length(alpha) == 1    error('alpha must be a vector');end% ensure x is is a vector of the same size as alphaif any(size(x) ~= size(alpha))    error('x and alpha must be the same size');end%-------------------------------------------------% Main%-------------------------------------------------if any(x < 0)    p = 0;elseif sum(x) ~= 1    disp(['dirichletpdf warning: sum(x)~=1, but this may be ' ...        'due to numerical issues']);    p = 0;else    z = gammaln(sum(alpha)) - sum(gammaln(alpha));     z = exp(z);    p = z * prod(x.^(alpha-1));end