coeffs()

Matrix * Matrix::coeffs	(	M2_arrayint	vars,
		const Matrix *	monoms ) const

Definition at line 1852 of file matrix.cpp.

{
  // Given an array_ of variable indices, 'vars', and given
  // that 'monoms' and 'this' both have one row, makes a matrix
  // having number of rows = ncols(monoms),
  //        number of cols = ncols(this),
  // whose (r,c) entry is the coefficient (in the other variables)
  // of this[0,c] in the monomial monoms[0,r].
 
  // Step 0: Do some error checking
  const PolynomialRing *P = get_ring()->cast_to_PolynomialRing();
  if (P != nullptr)
    {
      int nvars = P->n_vars();
      int nelements = monoms->n_cols();
      if (monoms->n_rows() != n_rows())
        {
          ERROR("expected matrices with the same number of rows");
          return nullptr;
        }
      for (unsigned int i = 0; i < vars->len; i++)
        if (vars->array[i] < 0 || vars->array[i] >= nvars)
          {
            ERROR("coeffs: expected a set of variable indices");
            return nullptr;
          }
 
      // Step 1: Make an exponent_table of all of the monoms.
      // We set the value of the i th monomial to be 'i+1', since 0
      // indicates a non-existent entry.
 
      // The extra size in monomial refers to the component:
      exponent_table *E = exponent_table_new(nelements, 1 + vars->len);
      exponent EXP = newarray_atomic(int, nvars);
      for (int i = 0; i < nelements; i++)
        {
          vec v = monoms->elem(i);
          if (v == nullptr)
            {
              ERROR("expected non-zero column");
              return nullptr;
            }
          ring_elem f = v->coeff;
          const_monomial m = P->lead_flat_monomial(f);
          P->getMonoid()->to_expvector(m, EXP);
 
          // grab only that part of the monomial we need
          exponent e = newarray_atomic(int, 1 + vars->len);
          get_part_of_expvector(vars, EXP, v->comp, e);
          exponent_table_put(E, e, i + 1);
        }
 
      // Step 2: for each vector column of 'this'
      //     create a column, and put this vector into result.
 
      MatrixConstructor mat(P->make_FreeModule(nelements), 0);
      for (int i = 0; i < n_cols(); i++)
        mat.append(coeffs_of_vec(E, vars, rows(), elem(i)));
 
      return mat.to_matrix();
    }
  const M2FreeAlgebraOrQuotient* Q = dynamic_cast<const M2FreeAlgebraOrQuotient*>(get_ring());
  if (Q != nullptr)
    {
      ModuleMonomialSet H(Q->n_vars());
      NCMonomials(H, monoms);
      return NCCoefficientMatrix(H, this);
    }
  ERROR("expected polynomial ring");
  return nullptr;
}

References MatrixConstructor::append(), coeffs(), coeffs_of_vec(), elem(), ERROR, exponent_table_new(), exponent_table_put(), get_part_of_expvector(), get_ring(), PolynomialRing::getMonoid(), PolynomialRing::lead_flat_monomial(), Ring::make_FreeModule(), Matrix(), MatrixConstructor, n_cols(), n_rows(), M2FreeAlgebraOrQuotient::n_vars(), PolynomialRing::n_vars(), NCCoefficientMatrix(), NCMonomials(), nelements, newarray_atomic, rows(), Monoid::to_expvector(), and MatrixConstructor::to_matrix().

Referenced by coeffs(), and rawCoefficients().