eigenvalues() [3/4]

bool Lapack::eigenvalues ( const DMatRR * A, DMatCC * eigenvals )

static

Definition at line 302 of file lapack.cpp.

{
  int size = static_cast<int>(A->numRows());
  if (size != static_cast<int>(A->numColumns()))
    {
      ERROR("expected a square matrix");
      return false;
    }
 
  if (size == 0)
    {
      eigvals->resize(0, 1);
      return true;
    }
 
  bool ret = true;
  char dont = 'N';
  int wsize = 3 * size;
  double* workspace = new double[2 * wsize];
  int info;
 
  std::vector<double> copyA = make_lapack_array(*A);
  double *real = new double[size]; // real components of eigvals
  double *imag = new double[size];  // imaginary components
 
  dgeev_(&dont,
         &dont,
         &size,
         copyA.data(),
         &size,
         real,
         imag,
         static_cast<double *>(nullptr),
         &size, /* left eigenvectors */
         static_cast<double *>(nullptr),
         &size, /* right eigenvectors */
         workspace,
         &wsize,
         &info);
 
  if (info < 0)
    {
      ERROR("argument passed to dgeev had an illegal value");
      ret = false;
    }
  else if (info > 0)
    {
      ERROR("the QR algorithm in dgeev failed to compute all eigvals");
      ret = false;
    }
  else
    {
      eigvals->resize(size, 1);
      for (int i = 0; i < size; i++)
        eigvals->ring().set_from_doubles(eigvals->entry(i, 0), real[i], imag[i]);
    }
 
  delete [] real;
  delete [] imag;
 
  return ret;
}

References dgeev_(), DMat< ACoeffRing >::entry(), ERROR, make_lapack_array(), DMat< ACoeffRing >::numColumns(), DMat< ACoeffRing >::numRows(), DMat< ACoeffRing >::resize(), DMat< ACoeffRing >::ring(), and M2::ARingCC::set_from_doubles().