eig_sym_d.cc

// -*- mode: c++; fill-column: 80; c-basic-offset: 2; indent-tabs-mode: nil -*-
/*
    Copyright (c) 2010 Juan Jose Garcia Ripoll

    Tensor is free software; you can redistribute it and/or modify it
    under the terms of the GNU Library General Public License as published
    by the Free Software Foundation; either version 2 of the License, or
    (at your option) any later version.

    This program is distributed in the hope that it will be useful,
    but WITHOUT ANY WARRANTY; without even the implied warranty of
    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
    GNU Library General Public License for more details.

    You should have received a copy of the GNU General Public License along
    with this program; if not, write to the Free Software Foundation, Inc.,
    51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
*/

#include <tensor/tensor.h>
#include <tensor/tensor_lapack.h>
#include <tensor/linalg.h>

namespace linalg {

  using namespace lapack;

  RTensor
  eig_sym(const RTensor &A, RTensor *V)
  {
    assert(A.rows() > 0);
    assert(A.rank() == 2);
    assert(A.rows() == A.columns());

    integer n = A.rows();
    if ((size_t)n != A.columns()) {
      std::cerr << "Routine eig_sym() can only compute eigenvalues of square matrices, and you\n"
                << "have passed a matrix that is " << A.rows() << " by " << A.columns();
      abort();
    }

    RTensor aux(A);
    double *a = tensor_pointer(aux);
    integer lda = n, info[1];
    char jobz[2] = { (V == 0)? 'N' : 'V', 0 };
    char uplo[2] = { 'U', 0 };
    RTensor output(n);
    double *w = tensor_pointer(output);

#ifdef TENSOR_USE_ACML
    dsyev(*jobz, *uplo, n, a, lda, w, info);
#else
    integer lwork = -1;
    double work0[1];
    F77NAME(dsyev)(jobz, uplo, &n, a, &lda, w, work0, &lwork, info);
    lwork = (int)work0[0];

    RTensor work(lwork);
    F77NAME(dsyev)(jobz, uplo, &n, a, &lda, w, tensor_pointer(work),
                   &lwork, info);
#endif

    if (V) *V = aux;
    return output;
  }

} // namespace linalg