mps-0.0.0
MatrixProductStatesinC++
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rmps_ghz_state.cc
1 // -*- mode: c++; fill-column: 80; c-basic-offset: 2; indent-tabs-mode: nil -*-
2 /*
3  Copyright (c) 2010 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 <algorithm>
21 #include <mps/mps.h>
22 
23 namespace mps {
24 
25  using namespace tensor;
26 
27  const RMPS ghz_state(index length, bool periodic)
28  {
29  RMPS output(length, 2, 2, periodic);
30  if (length == 1) {
31  double v = 1.0/sqrt(2.0);
32  RTensor &aux = output.at(0);
33  aux.fill_with_zeros();
34  if (periodic) {
35  aux.at(0,1,0) = v;
36  aux.at(1,1,1) = v;
37  } else {
38  aux.at(0,0,0) = v;
39  aux.at(0,1,0) = v;
40  }
41  } else {
42  double v = 1.0/sqrt(sqrt(2.0));
43  for (size_t i = 0; i < length; i++) {
44  RTensor &aux = output.at(i);
45  aux.fill_with_zeros();
46  if (i == 0) {
47  aux.at(0,0,0) = v;
48  aux.at((periodic?1:0),1,1) = v;
49  } else if (i == (length-1)) {
50  aux.at(0,0,0) = v;
51  aux.at(1,1,(periodic?1:0)) = v;
52  } else {
53  aux.at(0,0,0) = 1.0;
54  aux.at(1,1,1) = 1.0;
55  }
56  }
57  }
58  return output;
59  }
60 
61 } // namespace mps
Real matrix product structure.
Definition: rmps.h:31
const RMPS ghz_state(index length, bool periodic=false)
Create a GHZ state.