mps-0.0.0
MatrixProductStatesinC++
 All Data Structures Namespaces Functions Variables Enumerations Enumerator Groups Pages
rmps_cluster_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 cluster_state(index length)
28  {
29  if (length < 3) {
30  return ghz_state(length);
31  } else {
32  RMPS output(length, 2, 2);
33  double v0 = 1.0/sqrt(sqrt(2.0));
34  double v = 1.0/sqrt(2.0);
35 
36  RTensor &P0 = output.at(0);
37  P0.fill_with_zeros();
38  P0.at(0,0,0) = P0.at(0,1,1) = v;
39 
40  RTensor &PL = output.at(length-1);
41  PL.at(0,0,0) = v;
42  PL.at(0,1,0) = v;
43  PL.at(1,0,0) = v;
44  PL.at(1,1,0) = -v;
45 
46  for (index i = 1; i < (length - 1); i++) {
47  RTensor &P = output.at(i);
48  P.fill_with_zeros();
49  P.at(0,0,0) = v;
50  P.at(1,0,0) = v;
51  P.at(0,1,1) = v;
52  P.at(1,1,1) = -(v);
53  }
54  return output;
55  }
56 }
57 
58 } // namespace mps
Real matrix product structure.
Definition: rmps.h:31
const RMPS ghz_state(index length, bool periodic=false)
Create a GHZ state.
const RMPS cluster_state(index length)
Create a cluster state.