exp_randomdev.h

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/*
 *  exp_randomdev.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 EXP_RANDOMDEV_H
#define EXP_RANDOMDEV_H

#include <cmath>
#include "randomgen.h"
#include "randomdev.h"
#include "lockptr.h"

namespace librandom {

/*BeginDocumentation
Name: rdevdict::exponential - exponential random deviate generator
Description: Generates exponentially distributed random numbers.

  p(x) = lambda exp(-lambda*x), x >= 0.     
    
Parameters: 
 lambda - rate parameter (default: 1.0)

SeeAlso: CreateRDV, RandomArray, rdevdict
Author: Hans Ekkehard Plesser
*/

  class ExpRandomDev : public RandomDev
  {

  public:

    // accept only lockPTRs for initialization,
    // otherwise creation of a lock ptr would 
    // occur as side effect---might be unhealthy
  ExpRandomDev(RngPtr r_in) : RandomDev(r_in), lambda_(1.0) {}
  ExpRandomDev() : RandomDev(), lambda_(1.0) {}                // threaded

    using RandomDev::operator();
    double operator()(RngPtr rthrd) const;   // threaded

    void set_status(const DictionaryDatum&);

    void get_status(DictionaryDatum&) const; 

  private:
    double lambda_;  
  };

  inline
  double ExpRandomDev::operator()(RngPtr rthrd) const
  {
    return -std::log(rthrd->drandpos()) / lambda_;
  }

}

# endif