CouenneRootQ.hpp

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/* $Id: CouenneRootQ.hpp 940 2013-01-13 19:49:02Z pbelotti $
 *
 * Name:    rootQ.hpp
 * Author:  Pietro Belotti
 * Purpose: find roots of polynomial Q^k(x) (see Liberti and Pantelides, 2003)
 *
 * (C) Carnegie-Mellon University, 2006-10.
 * This file is licensed under the Eclipse Public License (EPL)
 */

#ifndef CouenneRootQ_hpp
#define CouenneRootQ_hpp

#include "CouenneTypes.hpp"
#include <map>
#include <iostream>

namespace Couenne
{

CouNumber rootQ (int k);



class Qroot {

 protected:


  static std::map <int, CouNumber> Qmap;

 public:

  Qroot  () {}

  ~Qroot () {}


  inline CouNumber operator () (int k) {

    std::map <int, CouNumber>:: iterator pos;
    CouNumber root;

    if( k % 2 == 1 )
    {
       k /= 2; // becomes true index

       if ((pos = Qmap.find (k)) == Qmap.end()) {

          std::pair <int, CouNumber> newpair;

          newpair.first  = k;
          newpair.second = (root = rootQ (k));

          Qmap.insert (newpair);
       }
       else
          root = pos -> second;
    }
    else
    {
       switch(k) {
          case 2: return -(sqrt(2.0) - 1.0);
          case 4: return -0.56042566045031785945;
          case 6: return -0.64146546982884663257;
          case 8: return -0.69428385661425826738;
          case 10: return -0.73192937842370733350;
          default:
             std::cerr << "Need to implement root finding for even k" << std::endl;
             throw -1;
       }
    }

    return root;
  }
};

}

#endif