ringmap.cpp

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// Copyright 1996  Michael E. Stillman
 
#include "ringmap.hpp"
#include "matrix.hpp"
#include "matrix-con.hpp"
#include "polyring.hpp"
#include "relem.hpp"
 
#include <iostream>
RingMap::RingMap(const Matrix *m) : R(m->get_ring())
{
  M = nullptr;
  P = R->cast_to_PolynomialRing();
  if (P != nullptr)
    {
      M = P->getMonoid();
      K = P->getCoefficientRing();
    }
  else
    K = R;
 
  nvars = m->n_cols();
  is_monomial = true;
 
  ring_elem one = K->from_long(1);
 
  // Allocate space for the ring map elements
  _elem = new var[nvars];
 
  for (int i = 0; i < nvars; i++)
    {
      // First initialize these fields:
      _elem[i].is_zero = false;
      _elem[i].coeff_is_one = true;
      _elem[i].monom_is_one = true;
      _elem[i].bigelem_is_one = true;
      _elem[i].coeff = ZERO_RINGELEM;
      _elem[i].monom = nullptr;
 
      ring_elem f = m->elem(0, i);  // This does a copy.
      _elem[i].bigelem = f;
 
      if (R->is_zero(f))
        _elem[i].is_zero = true;
      else if (P == nullptr)
        {
          // Not a polynomial ring, so put everything into coeff
          if (!K->is_equal(f, one))
            {
              _elem[i].coeff_is_one = false;
              _elem[i].coeff = K->copy(f);
            }
        }
      else
        {
// A polynomial ring.
#ifdef DEVELOPMENT
#warning "also handle fraction rings"
#endif
          Nterm *t = f;
          if (t->next == nullptr)
            {
              // This is a single term
              if (!K->is_equal(t->coeff, one))
                {
                  _elem[i].coeff_is_one = false;
                  _elem[i].coeff = K->copy(t->coeff);
                }
 
              if (!M->is_one(t->monom))  // should handle M->n_vars() == 0 case
                                         // correctly.
                {
                  _elem[i].monom_is_one = false;
                  _elem[i].monom = M->make_new(t->monom);
                }
            }
          else
            {
              // This is a bigterm
              is_monomial = false;
              _elem[i].bigelem_is_one = false;
            }
        }
      K->remove(one);
    }
}
 
RingMap::~RingMap()
{
  for (int i = 0; i < nvars; i++)
    {
      if (!_elem[i].coeff_is_one) K->remove(_elem[i].coeff);
      if (!_elem[i].monom_is_one) M->remove(_elem[i].monom);
      R->remove(_elem[i].bigelem);
    }
  freemem(_elem);
  K = nullptr;
  M = nullptr;
}
 
unsigned int RingMap::computeHashValue() const
{
  unsigned int hashval = 4565 * get_ring()->hash();
  for (int i = 0; i < nvars; i++)
    {
      hashval =
          46343 * hashval + get_ring()->computeHashValue(_elem[i].bigelem);
    }
  return hashval;
}
bool RingMap::is_equal(const RingMap *phi) const
{
  // Two ringmap's are identical if their 'bigelem's are the same
  if (R != phi->get_ring()) return false;
  if (nvars != phi->nvars) return false;
 
  for (int i = 0; i < nvars; i++)
    if (!R->is_equal(elem(i), phi->elem(i))) return false;
 
  return true;
}
 
const RingMap *RingMap::make(const Matrix *m)
{
  RingMap *result = new RingMap(m);
  return result;
}
 
void RingMap::text_out(buffer &o) const
{
  o << "(";
  for (int i = 0; i < nvars; i++)
    {
      if (i > 0) o << ", ";
      R->elem_text_out(o, _elem[i].bigelem);
    }
  o << ")";
}
 
ring_elem RingMap::eval_term(const Ring *sourceK,  // source coeff ring
                             const ring_elem a,  // coefficient of term
                             const_varpower vp,
                             int first_var,
                             int nvars_in_source) const
{
  for (index_varpower i = vp; i.valid(); ++i)
    {
      int v = first_var + i.var();
      if (v >= nvars || _elem[v].is_zero)
        return R->from_long(0);  // The result is zero.
    }
 
  // If K is a coeff ring of R, AND map is an identity on K,
  // then don't recurse: use this value directly.
  // Otherwise, we must recurse, I guess.
  ring_elem result = sourceK->eval(this, a, first_var + nvars_in_source);
  if (R->is_zero(result)) return result;
 
  monomial result_monom = nullptr;
  monomial temp_monom = nullptr;
  ring_elem result_coeff = K->from_long(1);
 
  if (P != nullptr)
    {
      result_monom = M->make_one();
      temp_monom = M->make_one();
    }
 
  if (!R->is_commutative_ring() || R->cast_to_SchurRing())
    {
      // This is the only non-commutative case so far
      for (index_varpower i = vp; i.valid(); ++i)
        {
          int v = first_var + i.var();
          int e = i.exponent();
          ring_elem g;
          if (e >= 0)
            g = _elem[v].bigelem;
          else
            g = R->invert(_elem[v].bigelem);
          for (int j = 0; j < e; j++)
            {
              assert(v < nvars);
              ring_elem tmp = R->mult(g, result);
              R->remove(result);
              result = tmp;
            }
        }
    }
  else
    {
      for (index_varpower i = vp; i.valid(); ++i)
        {
          int v = first_var + i.var();
          int e = i.exponent();
          assert(v < nvars);
          if (_elem[v].bigelem_is_one && e > 0)
            {
              if (!_elem[v].coeff_is_one)
                {
                  ring_elem tmp = K->power(_elem[v].coeff, e);
                  K->mult_to(result_coeff, tmp);
                  K->remove(tmp);
                }
              if (!_elem[v].monom_is_one)
                {
                  M->power(_elem[v].monom, e, temp_monom);
                  M->mult(result_monom, temp_monom, result_monom);
                }
            }
          else
            {
              ring_elem thispart = R->power(_elem[v].bigelem, e);
              R->mult_to(result, thispart);
              R->remove(thispart);
              if (R->is_zero(result)) break;
            }
        }
      if (P != nullptr)
        {
          ring_elem temp = P->make_flat_term(result_coeff, result_monom);
          K->remove(result_coeff);
          M->remove(result_monom);
          M->remove(temp_monom);
          P->mult_to(result, temp);
          P->remove(temp);
        }
      else
        {
          // result_monom has not been used
          // and result, result_coeff are both in the ring K
          result = K->mult(result, result_coeff);
        }
    }
  return result;
}
 
RingElement /* or null */ *RingMap::eval(const RingElement *r) const
{
  RingElement *result = RingElement::make_raw(
      get_ring(), r->get_ring()->eval(this, r->get_value(), 0));
  if (error()) return nullptr;
  return result;
}
 
Matrix /* or null */ *RingMap::eval(const FreeModule *F, const Matrix *m) const
{
  MatrixConstructor mat(F, 0);
  for (int i = 0; i < m->n_cols(); i++)
    mat.append(m->get_ring()->vec_eval(this, F, m->elem(i)));
  if (error()) return nullptr;
  return mat.to_matrix();
}
 
// Local Variables:
// compile-command: "make -C $M2BUILDDIR/Macaulay2/e "
// indent-tabs-mode: nil
// End: