Alexandria  2.22.0
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NeihbourhoodFunc.cpp
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1 /*
2  * Copyright (C) 2012-2021 Euclid Science Ground Segment
3  *
4  * This library is free software; you can redistribute it and/or modify it under
5  * the terms of the GNU Lesser General Public License as published by the Free
6  * Software Foundation; either version 3.0 of the License, or (at your option)
7  * any later version.
8  *
9  * This library is distributed in the hope that it will be useful, but WITHOUT
10  * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS
11  * FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public License for more
12  * details.
13  *
14  * You should have received a copy of the GNU Lesser General Public License
15  * along with this library; if not, write to the Free Software Foundation, Inc.,
16  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
17  */
18 
19 #include "SOM/NeighborhoodFunc.h"
20 #include <cmath>
21 #include <algorithm> // std::max
22 
23 namespace Euclid {
24 namespace SOM {
25 namespace NeighborhoodFunc {
26 
27 Signature linearUnitDisk(double initial_radius) {
28  double r_square = initial_radius * initial_radius;
30  std::size_t iteration, std::size_t total_iterations) -> double {
31  double iter_factor = 1.0 * (total_iterations - iteration) / total_iterations;
32  iter_factor = iter_factor * iter_factor; // We compare the squared distances
33  double x = bmu.first - cell.first;
34  double y = bmu.second - cell.second;
35  double dist_square = x * x + y * y;
36  if (dist_square < r_square * iter_factor) {
37  return 1.;
38  } else {
39  return 0.;
40  }
41  };
42 }
43 
44 Signature kohonen(std::size_t x_size, std::size_t y_size, double sigma_cutoff_mult) {
45 
46  double init_sigma = std::max(x_size, y_size) / 2.;
47  std::tuple<std::size_t, std::size_t, double> sigma_buffer{0, 0, 0.};
48  double cutoff_mult_square = sigma_cutoff_mult * sigma_cutoff_mult;
49 
50  return [init_sigma, sigma_buffer, cutoff_mult_square](std::pair<std::size_t, std::size_t> bmu,
52  std::size_t total_iterations) mutable -> double {
53  // If we have new iteration we recompute the sigma, otherwise we use the already
54  // calculated one
55  if (std::get<0>(sigma_buffer) != iteration || std::get<1>(sigma_buffer) != total_iterations) {
56  std::get<0>(sigma_buffer) = iteration;
57  std::get<1>(sigma_buffer) = total_iterations;
58  double time_constant = total_iterations / std::log(init_sigma);
59  std::get<2>(sigma_buffer) = init_sigma * std::exp(-1. * iteration / time_constant);
60  }
61  double sigma_square = std::get<2>(sigma_buffer) * std::get<2>(sigma_buffer);
62 
63  double x = static_cast<double>(bmu.first) - cell.first;
64  double y = static_cast<double>(bmu.second) - cell.second;
65  double dist_square = x * x + y * y;
66 
67  if (dist_square < cutoff_mult_square * sigma_square) {
68  return std::exp(-1. * dist_square / (2. * sigma_square));
69  } else {
70  return 0.;
71  }
72  };
73 }
74 
75 } // namespace NeighborhoodFunc
76 } // namespace SOM
77 } // namespace Euclid
T exp(T... args)
T log(T... args)
T max(T... args)
ELEMENTS_API Signature linearUnitDisk(double initial_radius)
ELEMENTS_API Signature kohonen(std::size_t x_size, std::size_t y_size, double sigma_cutoff_mult=1.)