Method compute_flip_variables

IntegerProgramming/matrix.cc:517–577

}

int matrix::compute_flip_variables(int*& F)
{
  // first compute nonzero vector
  int okay=compute_nonzero_kernel_vector();

  if(!okay)
  {
    cout<<"\nWARNING: int matrix::compute_flip_variables(int*&):\n"
      "kernel of the matrix contains no vector with nonzero components,\n"
      "no flip variables computed"<<endl;
    return -1;
  }

  // compute variables to flip; these might either be those corresponding
  // to the positive components of the kernel vector without zero components
  // or those corresponding to the negative ones

  int r=0;
  // number of flip variables

  for(int j=0;j<columns;j++)
    if(H[0][j]<BigInt(0))
      r++;
  // remember that all components of H[0] are !=0

  if(r==0)
    // no flip variables
    return 0;

  if(2*r>columns)
    // more negative than positive components in H[0]
    // all variables corresponding to positive components will be flipped
  {
    r=columns-r;
    F=new int[r];
    memset(F,0,r*sizeof(int));
    int counter=0;
    for(int j=0;j<columns;j++)
      if(H[0][j]> BigInt(0))
      {
        F[counter]=j;
        counter++;
      }
  }
  else
    // more (or as many) positive than negative components in v
    // all variables corresponding to negative components will be flipped
  {
    F=new int[r];
    memset(F,0,r*sizeof(int));
    int counter=0;
    for(int j=0;j<columns;j++)
      if(H[0][j]< BigInt(0))
      {
        F[counter]=j;
        counter++;
      }
  }