expression.h

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//
// APFEL++ 2017
//
// Author: Valerio Bertone: valerio.bertone@cern.ch
//
 
#pragma once
 
namespace apfel
{
  class Expression
  {
  public:
    virtual ~Expression() = default;
 
 
    Expression(double const& eta = 1);
 
 
    virtual double Regular(double const&) const { return 0; }
 
    virtual double Singular(double const&) const { return 0; }
 
    virtual double Local(double const&) const { return 0; }
 
    virtual double LocalPP(double const&) const { return 0; }
 
    virtual double SingularPV(double const&) const { return 0; }
 
    virtual double LocalPV(double const&) const { return 0; }
 
    void SetExternalVariable(double const& extvar) const { _extvar = extvar; }
 
    double eta() const { return _eta; }
 
  protected:
    double mutable _extvar;  
    double const   _eta;     
  };
 
 
  class Identity: public Expression
  {
  public:
    Identity(): Expression() { }
    double Local(double const&) const { return 1; }
  };
 
  class Null: public Expression
  {
  public:
    Null(): Expression() { }
  };
}