reducedgb-field.cpp

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// Copyright 2005, Michael E. Stillman
 
#include "reducedgb-field.hpp"
#include "monideal.hpp"
#include <functional>
#include <algorithm>
 
ReducedGB_Field::~ReducedGB_Field()
{
  delete T;
  Rideal = nullptr;
}
 
void ReducedGB_Field::set_gb(VECTOR(POLY) & polys0) { (void) polys0; }
struct ReducedGB_Field_sorter
{
  GBRing *R;
  const FreeModule *F;
  const VECTOR(POLY) & gb;
  ReducedGB_Field_sorter(GBRing *R0,
                         const FreeModule *F0,
                         const VECTOR(POLY) & gb0)
      : R(R0), F(F0), gb(gb0)
  {
  }
  bool operator()(int xx, int yy)
  {
    gbvector *x = gb[xx].f;
    gbvector *y = gb[yy].f;
    return R->gbvector_compare(F, x, y) == LT;
  }
};
 
ReducedGB_Field::ReducedGB_Field(GBRing *R0,
                                 const PolynomialRing *originalR0,
                                 const FreeModule *F0,
                                 const FreeModule *Fsyz0)
  : ReducedGB(R0, originalR0, F0, Fsyz0), T(nullptr), Rideal(nullptr)
{
  T = MonomialTable::make(R0->n_vars());
  if (originalR->is_quotient_ring())
    Rideal = originalR->get_quotient_monomials();
}
 
void ReducedGB_Field::minimalize(const VECTOR(POLY) & polys0, bool auto_reduced)
// I have to decide: does this ADD to the existing set?
{
  // First sort these elements via increasing lex order (or monomial order?)
  // Next insert minimal elements into T, and polys
 
  VECTOR(int) positions;
  positions.reserve(polys0.size());
 
  for (int i = 0; i < polys0.size(); i++) positions.push_back(i);
 
  //  displayElements("-- before sort --", R, polys0, [](auto& g) { return g.f;
  //  } );
 
  std::stable_sort(
      positions.begin(), positions.end(), ReducedGB_Field_sorter(R, F, polys0));
 
  //  VECTOR(gbvector*) sorted_elements_debug_only;
  //  for (int i=0; i<positions.size(); i++)
  //    sorted_elements_debug_only.push_back(polys0[positions[i]].f);
  //  displayElements("-- after sort --", R, sorted_elements_debug_only,
  //  [](auto& g) { return g; } );
 
  // Now loop through each element, and see if the lead monomial is in T.
  // If not, add it in , and place element into 'polys'.
 
  for (VECTOR(int)::iterator i = positions.begin(); i != positions.end(); i++)
    {
      Bag *not_used;
      gbvector *f = polys0[*i].f;
      exponents_t e = R->exponents_make();
      R->gbvector_get_lead_exponents(F, f, e);
      if ((!Rideal || !Rideal->search_expvector(e, not_used)) &&
          T->find_divisors(1, e, f->comp) == 0)
        {
          // Keep this element
 
          POLY h;
          ring_elem junk;
 
          h.f = R->gbvector_copy(f);
          h.fsyz = R->gbvector_copy(polys0[*i].fsyz);
 
          if (auto_reduced) remainder(h, false, junk);  // This auto-reduces h.
 
          R->gbvector_remove_content(h.f, h.fsyz);
 
          T->insert(e, f->comp, INTSIZE(polys));
          polys.push_back(h);
        }
      else
        R->exponents_delete(e);
    }
}
 
void ReducedGB_Field::remainder(POLY &f, bool use_denom, ring_elem &denom)
{
  gbvector head;
  gbvector *frem = &head;
  frem->next = nullptr;
  POLY h = f;
  exponents_t EXP = ALLOCATE_EXPONENTS(R->exponent_byte_size());
 
  while (!R->gbvector_is_zero(h.f))
    {
      R->gbvector_get_lead_exponents(F, h.f, EXP);
      int x = h.f->comp;
      Bag *b;
      if (Rideal != nullptr && Rideal->search_expvector(EXP, b))
        {
          const gbvector *g = originalR->quotient_gbvector(b->basis_elem());
          R->gbvector_reduce_lead_term(
              F, Fsyz, head.next, h.f, h.fsyz, g, nullptr, use_denom, denom);
        }
      else
        {
          int w = T->find_divisor(EXP, x);
          if (w >= 0)
            {
              POLY g = polys[w];
              R->gbvector_reduce_lead_term(F,
                                           Fsyz,
                                           head.next,
                                           h.f,
                                           h.fsyz,
                                           g.f,
                                           g.fsyz,
                                           use_denom,
                                           denom);
            }
          else
            {
              frem->next = h.f;
              frem = frem->next;
              h.f = h.f->next;
              frem->next = nullptr;
            }
        }
    }
  
  h.f = head.next;
 
  ring_elem denom1;
  ring_elem one_elem = R->get_flattened_coefficients()->one();
  denom1 = R->get_flattened_coefficients()->one(); // is replaced on next line
  originalR->get_quotient_info()->gbvector_normal_form(
                                                       Fsyz, h.fsyz, true, denom1);
  if (EQ != R->get_flattened_coefficients()->compare_elems(denom1, one_elem))
    {
      // multiply h.f by denom1.
      R->gbvector_mult_by_coeff_to(h.f, denom1);
    }
  if (use_denom)
    {
      R->get_flattened_coefficients()->mult_to(denom, denom1);
    }
  
  f.f = h.f;
  f.fsyz = h.fsyz;
}
 
void ReducedGB_Field::remainder(gbvector *&f, bool use_denom, ring_elem &denom)
{
  gbvector *zero = nullptr;
  gbvector head;
  gbvector *frem = &head;
  frem->next = nullptr;
  gbvector *h = f;
  exponents_t EXP = ALLOCATE_EXPONENTS(R->exponent_byte_size());
  while (!R->gbvector_is_zero(h))
    {
      R->gbvector_get_lead_exponents(F, h, EXP);
      int x = h->comp;
      Bag *b;
      if (Rideal != nullptr && Rideal->search_expvector(EXP, b))
        {
          const gbvector *g = originalR->quotient_gbvector(b->basis_elem());
          R->gbvector_reduce_lead_term(
              F, Fsyz, head.next, h, zero, g, zero, use_denom, denom);
        }
      else
        {
          int w = T->find_divisor(EXP, x);
          if (w < 0)
            {
              frem->next = h;
              frem = frem->next;
              h = h->next;
              frem->next = nullptr;
            }
          else
            {
              POLY g = polys[w];
              R->gbvector_reduce_lead_term(
                  F, Fsyz, head.next, h, zero, g.f, zero, use_denom, denom);
            }
        }
    }
  h = head.next;
  // R->gbvector_remove_content(h, 0, use_denom, denom);
  f = h;
}
 
// Local Variables:
// compile-command: "make -C $M2BUILDDIR/Macaulay2/e "
// indent-tabs-mode: nil
// End: