beta_normalization_factor.h

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/*
 *  beta_normalization_factor.h
 *
 *  This file is part of NEST.
 *
 *  Copyright (C) 2004 The NEST Initiative
 *
 *  NEST 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.
 *
 *  NEST 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 NEST.  If not, see <http://www.gnu.org/licenses/>.
 *
 */
 
#ifndef BETA_NORMALIZATION_FACTOR_H
#define BETA_NORMALIZATION_FACTOR_H
 
#include <cmath>
#include <limits>
 
// Includes from libnestutil
#include "numerics.h"
 
namespace nest
{
 
inline double
beta_normalization_factor( const double tau_rise, const double tau_decay )
{
  const double tau_difference = tau_decay - tau_rise;
  double peak_value = 0;
  if ( std::abs( tau_difference ) > std::numeric_limits< double >::epsilon() )
  {
    // peak time
    const double t_peak = tau_decay * tau_rise * std::log( tau_decay / tau_rise ) / tau_difference;
    // another denominator is computed here to check that it is != 0
    peak_value = std::exp( -t_peak / tau_decay ) - std::exp( -t_peak / tau_rise );
  }
  if ( std::abs( peak_value ) < std::numeric_limits< double >::epsilon() )
  {
    // if rise time == decay time use alpha function
    return numerics::e / tau_decay;
  }
  else
  {
    // if rise time != decay time use beta function
    return ( 1. / tau_rise - 1. / tau_decay ) / peak_value;
  }
}
 
}  // of namespace nest
 
 
#endif /* BETA_NORMALIZATION_FACTOR_H */