mps-0.0.0
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entropy.cc
1 // -*- mode: c++; fill-column: 80; c-basic-offset: 2; indent-tabs-mode: nil -*-
2 /*
3  Copyright (c) 2012 Juan Jose Garcia Ripoll
4 
5  Tensor is free software; you can redistribute it and/or modify it
6  under the terms of the GNU Library General Public License as published
7  by the Free Software Foundation; either version 2 of the License, or
8  (at your option) any later version.
9 
10  This program is distributed in the hope that it will be useful,
11  but WITHOUT ANY WARRANTY; without even the implied warranty of
12  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
13  GNU Library General Public License for more details.
14 
15  You should have received a copy of the GNU General Public License along
16  with this program; if not, write to the Free Software Foundation, Inc.,
17  51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
18 */
19 
20 #include <tensor/linalg.h>
21 #include <mps/quantum.h>
22 
23 namespace mps {
24 
31  double entropy(const RTensor &t)
32  {
33  if (t.rank() == 1) {
34  const RTensor &l = t;
35  double ltot = tensor::abs(sum(l)), s = 0.0;
36  for (size_t i = 0; i < l.size(); i++) {
37  double li = tensor::abs(l[i]) / ltot;
38  s -= li * log(li);
39  }
40  return s;
41  } else if (t.rank() == 2) {
42  return entropy(linalg::eig_sym(t));
43  } else {
44  assert(t.rank() == 1 || t.rank() == 2);
45  abort();
46  }
47  }
48 
49 }
double entropy(const RTensor &lambdas)
Compute the von Neumann entropy.
Definition: entropy.cc:31