Method drop_last_weighted_variable

IntegerProgramming/binomial.cc:1449–1527

BOOLEAN binomial::drop_last_weighted_variable(const term_ordering& w)
{
  _number_of_variables--;
  // dangerous!!

  // 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];

  short last_weighted_variable=w.number_of_weighted_variables()-1;
  aux[last_weighted_variable]=0;
  // set last component to zero, so it cannot influence the weight

  if(w.weight(aux)>=0)
  {
    for(short i=0;i<last_weighted_variable;i++)
      exponent_vector[i]=aux[i];
    for(short i=last_weighted_variable;i<_number_of_variables;i++)
      exponent_vector[i]=aux[i+1];
  }
  else
  {
    for(short i=0;i<last_weighted_variable;i++)
      exponent_vector[i]=-aux[i];
     for(short i=last_weighted_variable;i<_number_of_variables;i++)
      exponent_vector[i]=-aux[i+1];
  }

  delete[] aux;


#ifdef SUPPORT_DRIVEN_METHODS

  // Recompute head and tail.
  // Normally, this routine is only called for binomials that do not involve
  // the variable to be dropped. 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
  // routines, 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<0)
      tail_support|=(1<<i);