BDF.h

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// $Id$
//==============================================================================
//==============================================================================
 
#ifndef _BDF_H_
#define _BDF_H_
 
#include <vector>
 
 
namespace TimeIntegration 
{
  class BDF
  {
  public:
    explicit BDF(int order = 0);
    virtual ~BDF() {}
 
    void setOrder(int order);
 
    int getOrder() const;
    int getActualOrder() const { return coefs.size() - degree; }
    short int getDegree() const { return degree; }
 
    bool advanceStep(double dt = 0.0, double dtn = 0.0);
 
    virtual const std::vector<double>& getCoefs() const;
 
    double operator[](int idx) const { return this->getCoefs()[idx]; }
 
    template<class T> T extrapolate(const std::vector<T>& values) const
    {
      const T& v0 = values.front();
      if (step > 1 && this->getActualOrder() == 2) // second order
        return 2.0*v0 - values[1];
      else // first order
        return v0;
    }
 
  protected:
    short int           degree; 
    int                 step;   
    std::vector<double> coefs;  
    std::vector<double> coefs1; 
  };
 
 
  class BDFD2 : public BDF
  {
  public:
    explicit BDFD2(int order = 2, int step_ = 0);
 
    const std::vector<double>& getCoefs() const override;
 
  protected:
    std::vector<double> coefs2; 
  };
}
 
#endif