binomial()

ring_elem WeylAlgebra::binomial ( int top, int bottom ) const

protected

Definition at line 227 of file weylalg.cpp.

{
  // This should be located elsewhere
  // Assumption: bottom <= top, top >= 0, bottom >= 0.
  if (bottom == 0) return K_->from_long(1);
  if (bottom == 1) return K_->from_long(top);
  if (top <= binomtop) return K_->from_long(binomtable[top][bottom]);
  ring_elem result = K_->from_long(1);
  for (int a = 0; a < bottom; a++)
    {
      ring_elem b = K_->from_long(top - a);
      ring_elem result1 = K_->mult(result, b);
      K_->remove(result);
      K_->remove(b);
      ring_elem c = K_->from_long(a + 1);
      result = K_->divide(result1, c);  // exact
      K_->remove(c);
    }
  return result;
}

References binomtable, binomtop, PolynomialRing::K_, and result().