nullSpace()

size_t ffpackInterface::nullSpace	(	const DMatZZpFFPACK &	A,
		DMatZZpFFPACK &	result_nullspace )

Definition at line 136 of file dmat.cpp.

{
  bool right_side = true;  // This function is written so that one could set
                           // right_side to false.
  // (It used to be a parameter).
 
  DMatZZpFFPACK N(mat);  // copy of mat
  size_t nr = mat.numRows();
  size_t nc = mat.numColumns();
 
  DMatZZpFFPACK::ElementType* nullspaceFFPACK = nullptr;
 
  size_t nullspace_dim;
  size_t nullspace_leading_dim;
 
  FFPACK::NullSpaceBasis(mat.ring().field(),
                         (right_side ? FFLAS::FflasRight : FFLAS::FflasLeft),
                         nr,
                         nc,
                         N.rowMajorArray(),
                         nc,
                         nullspaceFFPACK,
                         nullspace_leading_dim,
                         nullspace_dim);
 
  //    std::cerr << "leading dim = " << nullspace_leading_dim << " and dim = "
  //    << nullspace_dim << std::endl;
  if (right_side && nullspace_dim != nullspace_leading_dim)
    {
      std::cerr << "error: this should not happen!" << std::endl;
    }
  else if (!right_side && nullspace_leading_dim != nc)
    {
      std::cerr << "error: this should not happen either!" << std::endl;
    }
 
  if (right_side)
    nullspace.resize(nc, nullspace_dim);
  else
    nullspace.resize(nullspace_dim, nr);
 
  std::swap(nullspace.rowMajorArray(), nullspaceFFPACK);
 
  delete[] nullspaceFFPACK;
  return nullspace_dim;
}

References DMatZZpFFPACK, and std::swap().

Referenced by DMatLinAlg< M2::ARingZZpFFPACK >::kernel().