invert()

ring_elem PolyRingQuotient::invert ( const ring_elem f ) const

virtual

Implements Ring.

Definition at line 161 of file polyquotient.cpp.

{
  if (nvars_ == 1 && n_quotients() == 1 && K_->is_field() && ! K_->is_fraction_field())
    {
      ring_elem g = quotient_element(0);
 
      RingElement *f1 = RingElement::make_raw(getAmbientRing(), f);
      RingElement *g1 = RingElement::make_raw(getAmbientRing(), g);
      const RingElement *u1;
      const RingElement *v1;
      const RingElement *ret = rawExtendedGCDRingElement(f1, g1, &u1, &v1);
      if (ret == nullptr)
        {
          // one reason this might return nullptr is if the coefficient ring is not
          // ZZ/n, ZZ, or QQ
          // now what do we do?
          // we can't return nullptr
          INTERNAL_ERROR("ring element gcd computation failed");
        }
      if (!getAmbientRing()->is_unit(ret->get_value())) return from_long(0);
      return u1->get_value();
    }
  else if (M_->numNonTermOrderVariables() == 0)
    return ann(from_long(1), f);
  else
    {
      // An error message is generated higher up
      return from_long(0);
    }
}

References ann(), from_long(), RingElement::get_value(), PolynomialRing::getAmbientRing(), INTERNAL_ERROR(), is_unit(), PolynomialRing::K_, PolynomialRing::M_, RingElement::make_raw(), PolynomialRing::n_quotients(), PolynomialRing::nvars_, PolynomialRing::quotient_element(), and rawExtendedGCDRingElement().

Referenced by is_unit().