coupling.h

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/*
 *  Copyright (C) 2002 Stefan Weinzierl
 *
 *  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; either version 2 of the License, or
 *  (at your option) any later version.
 *
 *  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
 */

#ifndef __PDF_COUPLING_H__
#define __PDF_COUPLING_H__

namespace pdf {

  class alpha_strong {

    // ctors

    // static functions
    public :
      static double beta_0(int Nf);
      static double beta_1(int Nf);

      static int get_active_flavours(double Q);
      static double get_lambda_QCD(double Q);
      static double get_lambda_QCD(int Nf);
      static double get_value(double Q, int Nf);

    private :
      static double get_F(double Q, double a_s, int Nf);
      static double get_dF(double Q, double a_s, int Nf);
      static double root_safeI(double a, double b, double Q, int Nf);

    // data members
    public :
      static double lambda_3;
      static double lambda_4;
      static double lambda_5;

      static double charm_threshold;
      static double bottom_threshold;

      static int method;

    // keywords
      enum {
        exact,
        truncate_in_one_over_L
      };

  };

} // namespace pdf

#endif // ndef __PDF_COUPLING_H__

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