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/* This file is part of the Gudhi Library. The Gudhi library
* (Geometric Understanding in Higher Dimensions) is a generic C++
* library for computational topology.
*
* Author: Francois Godi
*
* Copyright (C) 2015 INRIA (France)
*
* This program is free software: you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation, either version 3 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 General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with this program. If not, see <http://www.gnu.org/licenses/>.
*/
#ifndef BOTTLENECK_H_
#define BOTTLENECK_H_
#include <gudhi/Graph_matching.h>
#include <cmath>
namespace Gudhi {
namespace bottleneck_distance {
/** \brief Function to use in order to compute the Bottleneck distance between two persistence diagrams (see Concepts).
* If the last parameter e is not 0 (default value if not explicited), you get an additive e-approximation.
*
* \ingroup bottleneck_distance
*/
template<typename Persistence_diagram1, typename Persistence_diagram2>
double compute(const Persistence_diagram1 &diag1, const Persistence_diagram2 &diag2, double e=0.) {
Persistence_graph g(diag1, diag2, e);
double b = g.bottleneck_alive();
if(b == std::numeric_limits<double>::infinity())
return std::numeric_limits<double>::infinity();
std::vector<double> sd;
if(e == 0.)
sd = g.sorted_distances();
long idmin = 0;
long idmax = e==0. ? sd.size() - 1 : g.diameter_bound()/e + 1;
// alpha can change the complexity
double alpha = std::pow(idmax, 0.25);
Graph_matching m(g);
Graph_matching biggest_unperfect(g);
while (idmin != idmax) {
long step = static_cast<long>((idmax - idmin) / alpha);
m.set_r(e == 0. ? sd.at(idmin + step) : e*(idmin + step));
while (m.multi_augment());
//The above while compute a maximum matching (according to the r setted before)
if (m.perfect()) {
idmax = idmin + step;
m = biggest_unperfect;
} else {
biggest_unperfect = m;
idmin = idmin + step + 1;
}
}
b = std::max(b, e == 0. ? sd.at(idmin) : e*(idmin));
return b;
}
} // namespace bottleneck_distance
} // namespace Gudhi
#endif // BOTTLENECK_H_
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