support()

M2_arrayintOrNull Matrix::support

(

)

const

Definition at line 922 of file matrix.cpp.

{
  const PolynomialRing *R = get_ring()->cast_to_PolynomialRing();
  if (R != nullptr)
  {
    int n = R->n_vars();
    int nsupp = 0;
    exponents_t exp = newarray_atomic(int, R->n_vars());
    exponents_t exp2 = newarray_atomic(int, R->n_vars());
    for (int i = 0; i < R->n_vars(); i++) exp[i] = exp2[i] = 0;
    for (int j = 0; j < n_cols(); j++)
      for (vec v = elem(j); v != nullptr; v = v->next)
        for (Nterm& f : v->coeff)
        {
          R->getMonoid()->to_expvector(f.monom, exp2);
          for (int k = 0; k < n; k++)
            if (exp2[k] != 0 && exp[k] == 0)
            {
              exp[k] = 1;
              if (++nsupp == n) goto out;
            }
        }
out:
    M2_arrayint result = M2_makearrayint(nsupp);
    int next = 0;
    for (int i = 0; i < n; i++)
      if (exp[i] > 0) result->array[next++] = i;
    freemem(exp);
    freemem(exp2);
    return result;
  }
 
  // FreeAlgebraOrQuotient matrix support
  const M2FreeAlgebraOrQuotient* Q = dynamic_cast<const M2FreeAlgebraOrQuotient*>(get_ring());
  if (Q != nullptr)
  {
    int n = Q->n_vars();
    int nsupp = 0;
    std::vector<int> exp,exp2;  // commutative code above uses newarray_atomic.  Is std::vector ok?
    for (int i = 0; i < n; i++) 
      exp.push_back(0);
    for (int j = 0; j < n_cols() && nsupp < n; j++)
      for (vec v = elem(j); v != nullptr && nsupp < n; v = v->next)
      {
        auto f = Q->toPoly(v->coeff);
        for (auto t = f->cbegin(); t != f->cend(); ++t)
        {
          Q->freeAlgebra().monoid().support(t.monom(),exp2);
          for (int k = 0; k < exp2.size(); k++)
          {
            if (exp[exp2[k]] == 0)
            {
              exp[exp2[k]] = 1;
              if (++nsupp == n) break;
            }
          }
        }
      }
 
    M2_arrayint result = M2_makearrayint(nsupp);
    int next = 0;
    for (int i = 0; i < n; i++)
      if (exp[i] > 0) result->array[next++] = i;
    //freemem(exp);
    //freemem(exp2);
    return result;    
  }
 
  ERROR("expected a polynomial ring");
  return nullptr;
}

References Nterm::coeff, elem(), ERROR, M2FreeAlgebraOrQuotient::freeAlgebra(), freemem(), get_ring(), PolynomialRing::getMonoid(), M2_makearrayint(), FreeAlgebra::monoid(), Nterm::monom, n_cols(), M2FreeAlgebraOrQuotient::n_vars(), PolynomialRing::n_vars(), newarray_atomic, result(), FreeMonoid::support(), support(), Monoid::to_expvector(), and M2FreeAlgebraOrQuotient::toPoly().

Referenced by rawMatrixIndices(), and support().