fvar_dif.cpp

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/*
Author: David Fournier
Copyright (c) 2008-2012 Regents of the University of California
*/

#include "fvar.hpp"

void DF_first_diference(void);

dvar_vector first_difference(const dvar_vector& x)
{
  if (x.size() <= 1)
  {
    cerr << "Error -- vector size too small"
             " in first_difference(const dvar_vector&)" << endl;
    ad_exit(1);
  }

  gradient_structure* gs = gradient_structure::_instance;
  DF_FILE* fp = gradient_structure::fp;

  gs->RETURN_ARRAYS_INCREMENT();
  int mmin=x.indexmin();
  int mmax=x.indexmax()-1;
  dvar_vector tmp(mmin,mmax);
  for (int i=mmin; i<=mmax; i++)
  {
    tmp.elem_value(i)=x.elem_value(i+1)-x.elem_value(i);
  }
  save_identifier_string("CE4");
  fp->save_dvar_vector_position(x);
  fp->save_dvar_vector_position(tmp);
  save_identifier_string("CE1");
  gs->GRAD_STACK1->set_gradient_stack(DF_first_diference);
  gs->RETURN_ARRAYS_DECREMENT();
  return(tmp);
}

void DF_first_diference(void)
{
  DF_FILE* fp = gradient_structure::fp;

  verify_identifier_string("CE1");
  dvar_vector_position tmp_pos=fp->restore_dvar_vector_position();
  dvar_vector_position x_pos=fp->restore_dvar_vector_position();
  verify_identifier_string("CE4");
  dvector dftmp=restore_dvar_vector_derivatives(tmp_pos);
  dvector dfx(x_pos.indexmin(),x_pos.indexmax());
  dfx.initialize();
  for (int i=dfx.indexmax()-1; i>=dfx.indexmin(); i--)
  {
    // tmp.elem_value(i)=x.elem_value(i+1)-x.elem_value(i);
       dfx.elem(i+1)+=dftmp.elem(i);
       dfx.elem(i)-=dftmp.elem(i);
  }
  dfx.save_dvector_derivatives(x_pos);
}