wolffd@0: function p = multipdf(x,theta)
wolffd@0: %MULTIPDF Multinomial probability density function.
wolffd@0: %   p = multipdf(x,theta) returns the probabilities of 
wolffd@0: %   vector x, under the multinomial distribution
wolffd@0: %   with parameter vector theta.
wolffd@0: %
wolffd@0: %   Author: David Ross
wolffd@0: 
wolffd@0: %--------------------------------------------------------
wolffd@0: % Check the arguments.
wolffd@0: %--------------------------------------------------------
wolffd@0: error(nargchk(2,2,nargin));
wolffd@0: 
wolffd@0: % make sure theta is a vector
wolffd@0: if ndims(theta) > 2 | all(size(theta) > 1)
wolffd@0:     error('theta must be a vector');
wolffd@0: end
wolffd@0: 
wolffd@0: % make sure x is of the appropriate size
wolffd@0: if ndims(x) > 2 | any(size(x) ~= size(theta))
wolffd@0:     error('columns of X must have same length as theta');
wolffd@0: end
wolffd@0: 
wolffd@0: 
wolffd@0: %--------------------------------------------------------
wolffd@0: % Main...
wolffd@0: %--------------------------------------------------------
wolffd@0: p = prod(theta .^ x);
wolffd@0: p = p .* factorial(sum(x)) ./ prod(factorial_v(x));
wolffd@0: 
wolffd@0: 
wolffd@0: %--------------------------------------------------------
wolffd@0: % Function factorial_v(x): computes the factorial function
wolffd@0: % on each element of x
wolffd@0: %--------------------------------------------------------
wolffd@0: function r = factorial_v(x)
wolffd@0: 
wolffd@0: if size(x,2) == 1
wolffd@0:     x = x';
wolffd@0: end
wolffd@0: 
wolffd@0: r = [];
wolffd@0: for y = x
wolffd@0:     r = [r factorial(y)];
wolffd@0: end