calc_det()

ring_elem DetComputation::calc_det ( size_t * r, size_t * c, int p )

private

Definition at line 387 of file det.cpp.

{
  if (p0 == 1) return M->elem(static_cast<int>(r[0]), static_cast<int>(c[0]));
  ring_elem answer = R->from_long(0);
 
  int negate = 1;
  for (int i = p0 - 1; i >= 0; i--)
    {
      std::swap(c[i], c[p0 - 1]);
      negate = !negate;
      ring_elem g =
          M->elem(static_cast<int>(r[p0 - 1]), static_cast<int>(c[p0 - 1]));
      if (R->is_zero(g))
        {
          R->remove(g);
          continue;
        }
      ring_elem h = calc_det(r, c, p0 - 1);
      ring_elem gh = R->mult(g, h);
      R->remove(g);
      R->remove(h);
      if (negate)
        R->subtract_to(answer, gh);
      else
        R->add_to(answer, gh);
    }
 
  // pulling out the columns has disordered c. Fix it.
 
  size_t temp = c[p0 - 1];
  for (size_t i = p0 - 1; i > 0; i--) c[i] = c[i - 1];
  c[0] = temp;
 
  return answer;
}

References calc_det(), M, R, and std::swap().

Referenced by calc_det(), and step().