Binomial.h

//===========================================================================
// GoTools - SINTEF Geometry Tools
//
// GoTools module: Implicitization, version 1.0
//
// Copyright (C) 2000-2007 SINTEF ICT, Applied Mathematics, Norway.
//
// This program is free software; you can redistribute it and/or          
// modify it under the terms of the GNU General Public License            
// as published by the Free Software Foundation version 2 of the License. 
//
// This program 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 General Public License for more details.                           
//
// You should have received a copy of the GNU General Public License      
// along with this program; if not, write to the Free Software            
// Foundation, Inc.,                                                      
// 59 Temple Place - Suite 330,                                           
// Boston, MA  02111-1307, USA.                                           
//
// Contact information: E-mail: tor.dokken@sintef.no                      
// SINTEF ICT, Department of Applied Mathematics,                         
// P.O. Box 124 Blindern,                                                 
// 0314 Oslo, Norway.                                                     
//
// Other licenses are also available for this software, notably licenses
// for:
// - Building commercial software.                                        
// - Building software whose source code you wish to keep private.        
//===========================================================================
#ifndef _BINOMIAL_H
#define _BINOMIAL_H


#include <vector>


namespace Go {



class Binomial {
public:
    typedef std::vector<double>::iterator iter;

    Binomial() : pascals_triangle(10)
    {
        for (int i = 0; i < 10; ++i)
            pascals_triangle[i].reserve(10);
        pascals_triangle.resize(1);
        pascals_triangle[0].resize(1);
        pascals_triangle[0][0] = 1.0;
    }
    Binomial(int n)
    {
        init(n);
    }

    double operator() (int n, int i)
    {
        if (i < 0 || i > n)
            return 0.0;
        if (int(pascals_triangle.size()) < n+1)
            expand(n);

        return pascals_triangle[n][i];
    }

    iter operator[] (int n)
    {
        if (int(pascals_triangle.size()) < n+1)
            expand(n);

        return pascals_triangle[n].begin();
    }

    double trinomial(int n, int i, int j)
    {
        if (i < 0 || i > n || j < 0 || j > n)
            return 0.0;
        if (int(pascals_triangle.size()) < n+1)
            expand(n);

        return pascals_triangle[n][i] * pascals_triangle[n-i][j];
    }

    double quadrinomial(int n, int i, int j, int k)
    {
        if (i < 0 || i > n || j < 0 || j > n || k < 0 || k > n)
            return 0;
        if (int(pascals_triangle.size()) < n+1)
            expand(n);
        
        return pascals_triangle[n][i]
            * pascals_triangle[n-i][j]
            * pascals_triangle[n-i-j][k];
    }

private:
    void init(int n);
    void expand(int n);

    std::vector<std::vector<double> > pascals_triangle;

};


} // namespace Go


#endif // _BINOMIAL_H

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