random_dirichlet.hpp

#ifndef PASTELSYS_RANDOM_DIRICHLET_HPP
#define PASTELSYS_RANDOM_DIRICHLET_HPP

#include "pastel/sys/random/random_dirichlet.h"
#include "pastel/sys/random/random_gamma.h"
#include "pastel/sys/vector/vector_compare.h"

namespace Pastel
{

    template <typename Real, integer N>
    Vector<Real, ModifyN<N, N - 1>::Result> randomDirichlet(
        const Vector<Real, N>& shape)
    {
        PENSURE(allGreater(shape, 0));

        integer n = shape.size() - 1;
        Vector<Real, ModifyN<N, N - 1>::Result> u(ofDimension(n));

        Real gammaSum = 0;
        for (integer i = 0;i < n;++i)
        {
            Real t = randomGamma<Real>(shape[i]);

            u[i] = t;
            gammaSum += t;
        }

        do
        {
            gammaSum += randomGamma<Real>(shape[n]);
        }
        while(gammaSum == 0);

        u /= gammaSum;

        return u;
    }

}

#endif