gbvector_cancel_lead_terms()

void GBRing::gbvector_cancel_lead_terms	(	const FreeModule *	F,
		const FreeModule *	Fsyz,
		const gbvector *	f,
		const gbvector *	fsyz,
		const gbvector *	g,
		const gbvector *	gsyz,
		gbvector *&	result,
		gbvector *&	result_syz )

Definition at line 1056 of file gbring.cpp.

{
  int comp;
  const ring_elem a = f->coeff;
  const ring_elem b = g->coeff;
  ring_elem u, v;
 
  exponents_t EXP1 = ALLOCATE_EXPONENTS(exp_size);
  exponents_t EXP2 = ALLOCATE_EXPONENTS(exp_size);
  exponents_t EXP3 = ALLOCATE_EXPONENTS(exp_size);
  exponents_t EXP4 = ALLOCATE_EXPONENTS(exp_size);
 
  monomial MONOM1 = ALLOCATE_MONOMIAL(monom_size);
  monomial MONOM2 = ALLOCATE_MONOMIAL(monom_size);
 
  K->syzygy(a, b, u, v);                    // If possible, u==1, anyway, u>0
  gbvector_get_lead_exponents(F, f, EXP1);  // Removes the Schreyer part
  gbvector_get_lead_exponents(F, g, EXP2);  // Removes the Schreyer part
  exponent_syzygy(EXP1, EXP2, EXP3, EXP4);
  if (g->comp == 0)
    comp = f->comp;
  else
    comp = 0;
  if (is_skew_commutative())
    {
      // Note that EXP3 * EXP1 = EXP4 * EXP2 up to sign
      if (_skew.mult_sign(EXP3, EXP1) != _skew.mult_sign(EXP4, EXP2))
        K->negate_to(v);
    }
  M->from_expvector(EXP3, MONOM1);
  M->from_expvector(EXP4, MONOM2);
  result = mult_by_term(F, f, u, MONOM1, 0);
  gbvector *result1 = mult_by_term(F, g, v, MONOM2, comp);
  gbvector_add_to(F, result, result1);
  if (fsyz == nullptr && gsyz == nullptr)
    result_syz = nullptr;
  else
    {
      result_syz = mult_by_term(Fsyz, fsyz, u, MONOM1, 0);
      gbvector *result_syz1 = mult_by_term(Fsyz, gsyz, v, MONOM2, comp);
      gbvector_add_to(Fsyz, result_syz, result_syz1);
    }
}

References _skew, ALLOCATE_EXPONENTS, ALLOCATE_MONOMIAL, gbvector::coeff, gbvector::comp, exp_size, exponent_syzygy(), gbvector_add_to(), gbvector_get_lead_exponents(), is_skew_commutative(), K, M, monom_size, mult_by_term(), and result().