Method drop_elimination_variables

IntegerProgramming/binomial.cc:1376–1444

BOOLEAN binomial::drop_elimination_variables(const term_ordering& w)
{
  _number_of_variables-=w.number_of_elimination_variables();
  // dangerous (no compatibility check)!!

  // copy components of interest to save memory
  // the leading term has to be recomputed!!

  Integer *aux=exponent_vector;
  exponent_vector=new Integer[_number_of_variables];

  if(w.weight(aux)>=0)
    for(short i=0;i<_number_of_variables;i++)
      exponent_vector[i]=aux[i];
  else
    for(short i=0;i<_number_of_variables;i++)
      exponent_vector[i]=-aux[i];

  delete[] aux;


#ifdef SUPPORT_DRIVEN_METHODS

  // Recompute head and tail.
  // Normally, this routine is only called for binomials that do not involve
  // the variables to eliminate. But if SUPPORT_VARIABLES_LAST is enabled,
  // the support changes in spite of this. Therefore, the support is
  // recomputed... For the same reasons as mentioned in the preceding
  // routine, the existing support information is not used.

  head_support=0;
  tail_support=0;
  short size_of_support_vectors=CHAR_BIT*sizeof(unsigned long);
  if(size_of_support_vectors>_number_of_variables)
    size_of_support_vectors=_number_of_variables;


#ifdef SUPPORT_VARIABLES_FIRST

  for(short i=0;i<size_of_support_vectors;i++)
  {
    Integer actual_entry=exponent_vector[i];
    if(actual_entry>0)
      head_support|=(1<<i);
    else if(actual_entry[i]<0)
      tail_support|=(1<<i);
  }

#endif  // SUPPORT_VARIABLES_FIRST


#ifdef SUPPORT_VARIABLES_LAST

  for(short i=0;i<size_of_support_vectors;i++)
  {
    Integer actual_entry=exponent_vector[_number_of_variables-1-i];
    if(actual_entry>0)
      head_support|=(1<<i);