/*
 *  gen_dirch.h	generating Dirichlet-distributed random vectors
 *  Copyright (C) 2000	Kevin Karplus
 *
 *  This library is free software; you can redistribute it and/or
 *  modify it under the terms of the GNU Lesser General Public
 *  License as published by the Free Software Foundation; 
 *  version 2.1 of the License.
 *
 *  This library is distributed in the hope that it will be useful,
 *  but WITHOUT ANY WARRANTY; without even the implied warranty of
 *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
 *  Lesser General Public License for more details.
 *
 *  See http://www.gnu.org/copyleft/lesser.html for the license details,
 *  or write to the Free Software Foundation, Inc., 59 Temple Place, Suite
 *  330, Boston, MA 02111-1307 USA
 */


/* This is a header file for a random number generator
 * that generates probability vectors according to a Dirichlet distribution.
 *
 * Kevin Karplus
 * 6 Nov 2000
 *
 * The functions here are made to look as much like a C++ class as
 * is possible in ANSI C.
 */


#ifndef GENDIRCHH
#define GENDIRCHH

#include "gen_beta.h"


// The sample from a Dirichlet distribution is generated by a tree of
// beta generators, each of which splits the probability passed down
// from above.
//
// The leaves of the tree are the num_dim places in the output
// probability vector (0..num_dim-1).
//
// The internal nodes of the tree are indicated by indexes >=num_dim.
// 


class gen_dirch
{
  private:
    int num_dim;	// number of dimensions of probability vector 
    double* alpha;	// 2*num_dim-1 alpha values 
			// First the leaves, then the internal nodes.
			 
    int root_index;
    gen_beta *betas;	// num_dim-1 internal nodes 
    int *left, *right;	// indexes of subtrees for internal nodes

    // store the alpha values and build a beta_tree for the generator 
    void initialize(int numd, const double *alp);
    void initialize(int numd, const float *alp);
	
    // Generate the probabilities for a subtree of the whole beta-tree
    // that defines the Dirichlet distribution, with the sum of the 
    // subtree being total_prob.
    void subtree(double *probs, double total_prob, int root) const;
    
  public:
  	gen_dirch(int numd, const double*alp) {initialize(numd,alp);}
  	gen_dirch(int numd, const float*alp) {initialize(numd,alp);}
	
	~gen_dirch(void)
	{   delete [] right;
	    delete [] left;
	    delete [] betas;
	    delete [] alpha;
	}
	
	// generate a probability vector according to the distribution and
	// store it in probs
	void generate(double *probs) const;

};

#endif

// CHANGE LOG:
// Fri Dec 14 11:44:30 PST 2007 Kevin Karplus
//	Mark Diekhans removed extraneous gen_dirch:: qualifier