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Diffstat (limited to 'example/Persistent_cohomology/plain_homology.cpp')
| -rw-r--r-- | example/Persistent_cohomology/plain_homology.cpp | 95 |
1 files changed, 95 insertions, 0 deletions
diff --git a/example/Persistent_cohomology/plain_homology.cpp b/example/Persistent_cohomology/plain_homology.cpp new file mode 100644 index 00000000..ae82c817 --- /dev/null +++ b/example/Persistent_cohomology/plain_homology.cpp @@ -0,0 +1,95 @@ +/* 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(s): Marc Glisse + * + * Copyright (C) 2015 INRIA Saclay - Ile-de-France (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/>. + */ + +#include <gudhi/Simplex_tree.h> +#include <gudhi/Persistent_cohomology.h> + +#include <iostream> +#include <vector> +#include <cstdint> // for std::uint8_t + +using namespace Gudhi; + +/* We could perfectly well use the default Simplex_tree<> (which uses + * Simplex_tree_options_full_featured), the following simply demonstrates + * how to save on storage by not storing a filtration value. */ + +struct MyOptions : Simplex_tree_options_full_featured { + // Implicitly use 0 as filtration value for all simplices + static const bool store_filtration = false; + // The persistence algorithm needs this + static const bool store_key = true; + // I have few vertices + typedef short Vertex_handle; + // Maximum number of simplices to compute persistence is 2^8 - 1 = 255. One is reserved for null_key + typedef std::uint8_t Simplex_key; +}; +typedef Simplex_tree<MyOptions> ST; + +int main() { + ST st; + + /* Complex to build. */ + /* 1 3 */ + /* o---o */ + /* /X\ / */ + /* o---o o */ + /* 2 0 4 */ + + const short triangle012[] = {0, 1, 2}; + const short edge03[] = {0, 3}; + const short edge13[] = {1, 3}; + const short vertex4[] = {4}; + st.insert_simplex_and_subfaces(triangle012); + st.insert_simplex_and_subfaces(edge03); + st.insert_simplex(edge13); + st.insert_simplex(vertex4); + // FIXME: Remove this line + st.set_dimension(2); + + // Sort the simplices in the order of the filtration + st.initialize_filtration(); + + // Class for homology computation + persistent_cohomology::Persistent_cohomology<ST, persistent_cohomology::Field_Zp> pcoh(st); + + // Initialize the coefficient field Z/2Z for homology + pcoh.init_coefficients(2); + + // Compute the persistence diagram of the complex + pcoh.compute_persistent_cohomology(); + + // Print the result. The format is, on each line: 2 dim 0 inf + // where 2 represents the field, dim the dimension of the feature. + // 2 0 0 inf + // 2 0 0 inf + // 2 1 0 inf + // means that in Z/2Z-homology, the Betti numbers are b0=2 and b1=1. + pcoh.output_diagram(); + + // Print the Betti numbers are b0=2 and b1=1. + std::cout << std::endl; + std::cout << "The Betti numbers are : "; + for (int i = 0; i < st.dimension(); i++) + std::cout << "b" << i << " = " << pcoh.betti_number(i) << " ; "; + std::cout << std::endl; +} |