tensor_trace.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>

namespace tensor {

  template<typename n>
  static void trace_loop(n *C, const n *D, index a1, index a2, index a3, index a4, index a5)
  {
    // C(a1,a3,a5), D(a1,a2,a3,a4,a5)
    // C(i,k,m) = sum D(i,l,k,l,m) over l
    index a2b = std::min(a2, a4);
    if (a1 == 1) {
      for (index m = 0; m < a5; m++) {
        for (index l = 0; l < a2b; l++) {
          for (index k = 0; k < a3; k++) {
            C[k + a3 * m] +=
                D[l + a2 * (k + a3 * (l + a4 * m))];
          }
        }
      }
    } else {
      for (index m = 0; m < a5; m++) {
        for (index l = 0; l < a2b; l++) {
          for (index k = 0; k < a3; k++) {
            for (index i = 0; i < a1; i++) {
              C[i + a1 * (k + a3 * m)] +=
                D[i + a1 * (l + a2 * (k + a3 * (l + a4 * m)))];
            }
          }
        }
      }
    }
  }

  template<typename elt_t>
  static const Tensor<elt_t> do_trace(const Tensor<elt_t> &D, index i1, index i2)
  {
    assert(i1 < D.rank() && i1 > -D.rank());
    assert(i2 < D.rank() && i2 > -D.rank());
    if (i1 < 0)
      i1 = i1 + D.rank();
    if (i2 < 0)
      i2 = i2 + D.rank();
    if (i1 > i2) {
      std::swap(i1,i2);
    } else if (i2 == i1) {
      std::cerr << "In trace(D, i, j), indices 'i' and 'j' are the same." << std::endl;
      abort();
    }

    index a1, a2, a3, a4, a5, i, rank;
    Indices dimensions(std::max(D.rank() - 2, 1));
    dimensions.at(rank=0) = 1;
    for (a1 = 1, i = 0; i < i1; ) {
      a1 *= (dimensions.at(rank++) = D.dimension(i++));
    }
    a2 = D.dimension(i++);
    for (a3 = 1; i < i2; )
      a3 *= (dimensions.at(rank++) = D.dimension(i++));
    a4 = D.dimension(i++);
    for (a5 = 1; i < D.rank(); )
      a5 *= (dimensions.at(rank++) = D.dimension(i++));

    Tensor<elt_t> output = RTensor::zeros(dimensions);
    trace_loop<elt_t>(output.begin(), D.begin(), a1, a2, a3, a4, a5);
    return output;
  }

} // namespace tensor