reduce_ZZ()

bool gbA::reduce_ZZ ( spair * p )

private

Definition at line 1453 of file gb-default.cpp.

{
  /* Returns false iff we defer computing this spair. */
  /* If false is returned, this routine has grabbed the spair 'p'. */
  int tmf, wt;
  int count = -1;
 
  exponents_t EXP = ALLOCATE_EXPONENTS(exp_size);
 
  if (M2_gbTrace == 15)
    {
      buffer o;
      o << "considering ";
      spair_text_out(o, p);
      o << " : ";
      emit_line(o.str());
    }
  compute_s_pair(p); /* Changes the type, possibly */
 
  while (!R->gbvector_is_zero(p->f()))
    {
      if (count++ > max_reduction_count)
        {
          spair_set_defer(p);
          return false;
        }
      if (M2_gbTrace >= 5)
        {
          if ((wt = weightInfo_->gbvector_weight(p->f(), tmf)) > this_degree)
            {
              buffer o;
              o << "ERROR: degree of polynomial is too high: deg " << wt
                << " termwt " << tmf << " expectedeg " << this_degree
                << newline;
              emit(o.str());
            }
        }
 
      int gap, w;
      R->gbvector_get_lead_exponents(_F, p->f(), EXP);
      int x = p->f()->comp;
      mpz_srcptr c = p->f()->coeff.get_mpz();
 
      w = find_good_term_divisor_ZZ(c, EXP, x, this_degree, gap);
 
      // If w < 0, then no divisor was found.  Is there a GB element of
      // the same degree as this one, and with the same exponent vector?
      // If so, use gcdextended to find (g,u,v),
      if (w < 0 || gap > 0)
        {
          MonomialTableZZ::mon_term *t =
              lookupZZ->find_exact_monomial(EXP, x, first_in_degree);
          if (t != nullptr)
            {
              // f <-- u*p+v*f (same with syz versions), need to change lookupZZ
              // too?
              // p <-- c*p-d*f
              gbelem *g = gb[t->_val];
              if (M2_gbTrace >= 10)
                {
                  buffer o;
                  o << "  swapping with GB element " << t->_val;
                  emit_line(o.str());
                }
 
              // If the element p is a generator, then we must assume that now
              // the
              // swapped g is a (possible) minimal generator.
              g->minlevel |= ELEM_MINGB;
              if (p->type == SPAIR::SPAIR_GEN || (g->minlevel & ELEM_MINGEN))
                {
                  g->minlevel |= ELEM_MINGEN;
                  p->type = SPAIR::SPAIR_GEN;
                }
 
              R->gbvector_replace_2by2_ZZ(
                  _F, _Fsyz, p->f(), p->fsyz(), g->g.f, g->g.fsyz);
              // Before continuing, do remainder of g->g
              replace_gb_element_ZZ(t);
 
              if (M2_gbTrace >= 10)
                {
                  buffer o;
                  o << "  swap yielded";
                  emit_line(o.str());
                  o.reset();
                  o << "      ";
                  R->gbvector_text_out(o, _F, p->f(), 3);
                  emit_line(o.str());
                  o.reset();
                  o << "      ";
                  R->gbvector_text_out(o, _F, g->g.f, 3);
                  emit_line(o.str());
                }
              continue;
            }
        }
 
      if (w < 0) break;
      if (gap > 0)
        {
          POLY h;
          h.f = R->gbvector_copy(p->x.f.f);
          h.fsyz = R->gbvector_copy(p->x.f.fsyz);
          insert_gb(h, (p->type == SPAIR::SPAIR_GEN ? ELEM_MINGEN : 0));
        }
      POLY g = gb[w]->g;
 
      R->gbvector_reduce_lead_term_ZZ(
          _F, _Fsyz, p->f(), p->fsyz(), g.f, g.fsyz);
      stats_nreductions++;
      if (M2_gbTrace == 15)
        {
          buffer o;
          o << "    reducing by g" << w;
          o << ", yielding ";
          R->gbvector_text_out(o, _F, p->f(), 3);
          emit_line(o.str());
        }
      if (R->gbvector_is_zero(p->f())) break;
      if (gap > 0)
        {
          p->deg += gap;
          if (M2_gbTrace == 15)
            {
              buffer o;
              o << "    deferring to degree " << p->deg;
              emit_line(o.str());
            }
          spair_set_insert(p);
          return false;
        }
    }
  if (M2_gbTrace >= 4 && M2_gbTrace != 15)
    {
      buffer o;
      o << "." << count;
      emit_wrapped(o.str());
    }
  return true;
}

References _F, _Fsyz, MonomialTableZZ::mon_term::_val, ALLOCATE_EXPONENTS, compute_s_pair(), ELEM_MINGB, ELEM_MINGEN, emit(), emit_line(), emit_wrapped(), exp_size, POLY::f, find_good_term_divisor_ZZ(), first_in_degree, POLY::fsyz, gbA::gbelem::g, gb(), insert_gb(), lookupZZ, M2_gbTrace, max_reduction_count, gbA::gbelem::minlevel, newline, p, POLY, R, replace_gb_element_ZZ(), buffer::reset(), SPAIR_GEN, spair_set_defer(), spair_set_insert(), spair_text_out(), stats_nreductions, buffer::str(), this_degree, weightInfo_, and x.

Referenced by reduceit().