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/* This file is part of the Gudhi Library - https://gudhi.inria.fr/ - which is released under MIT.
* See file LICENSE or go to https://gudhi.inria.fr/licensing/ for full license details.
* Author(s): Siargey Kachanovich
*
* Copyright (C) 2019 Inria
*
* Modification(s):
* - YYYY/MM Author: Description of the modification
*/
#ifndef PERMUTAHEDRAL_REPRESENTATION_FACE_FROM_INDICES_H_
#define PERMUTAHEDRAL_REPRESENTATION_FACE_FROM_INDICES_H_
#include <cstdlib> // for std::size_t
#include <algorithm>
namespace Gudhi {
namespace coxeter_triangulation {
/** \brief Computes the permutahedral representation of a face of a given simplex
* and a range of the vertex indices that compose the face.
*
* \tparam Permutahedral_representation has to be Permutahedral_representation
* \tparam Index_range is a range of unsigned integers taking values in 0,...,k,
* where k is the dimension of the simplex simplex.
*
* @param[in] simplex Input simplex.
* @param[in] indices Input range of indices.
*/
template <class Permutahedral_representation, class Index_range>
Permutahedral_representation face_from_indices(const Permutahedral_representation& simplex,
const Index_range& indices) {
using range_index = typename Index_range::value_type;
using Ordered_set_partition = typename Permutahedral_representation::OrderedSetPartition;
using Part = typename Ordered_set_partition::value_type;
using part_index = typename Part::value_type;
Permutahedral_representation value;
std::size_t d = simplex.vertex().size();
value.vertex() = simplex.vertex();
std::size_t k = indices.size() - 1;
value.partition().resize(k + 1);
std::size_t l = simplex.partition().size() - 1;
for (std::size_t h = 1; h < k + 1; h++)
for (range_index i = indices[h - 1]; i < indices[h]; i++)
for (part_index j : simplex.partition()[i]) value.partition()[h - 1].push_back(j);
for (range_index i = indices[k]; i < l + 1; i++)
for (part_index j : simplex.partition()[i]) value.partition()[k].push_back(j);
for (range_index i = 0; i < indices[0]; i++)
for (part_index j : simplex.partition()[i]) {
if (j != d)
value.vertex()[j]++;
else
for (std::size_t l = 0; l < d; l++) value.vertex()[l]--;
value.partition()[k].push_back(j);
}
// sort the values in each part (probably not needed)
for (auto& part : value.partition()) std::sort(part.begin(), part.end());
return value;
}
} // namespace coxeter_triangulation
} // namespace Gudhi
#endif
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