From 55c7181126aa7defce38c9b82872d14223d4c1dd Mon Sep 17 00:00:00 2001
From: Gard Spreemann <gspreemann@gmail.com>
Date: Tue, 7 Feb 2017 17:33:01 +0100
Subject: Initial import of upstream's 1.3.1.

---
 GudhUI/utils/Vertex_collapsor.h | 88 +++++++++++++++++++++++++++++++++++++++++
 1 file changed, 88 insertions(+)
 create mode 100644 GudhUI/utils/Vertex_collapsor.h

(limited to 'GudhUI/utils/Vertex_collapsor.h')

diff --git a/GudhUI/utils/Vertex_collapsor.h b/GudhUI/utils/Vertex_collapsor.h
new file mode 100644
index 00000000..2b36cb3a
--- /dev/null
+++ b/GudhUI/utils/Vertex_collapsor.h
@@ -0,0 +1,88 @@
+/* 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):       David Salinas
+ *
+ *    Copyright (C) 2014  INRIA Sophia Antipolis-Mediterranee (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 UTILS_VERTEX_COLLAPSOR_H_
+#define UTILS_VERTEX_COLLAPSOR_H_
+
+#include <list>
+
+#include "utils/Edge_contractor.h"
+#include "utils/Furthest_point_epsilon_net.h"
+#include "utils/UI_utils.h"
+
+/**
+ * Iteratively puts every vertex at the center of its neighbors
+ */
+template<typename SkBlComplex> class Vertex_collapsor {
+ private:
+  SkBlComplex& complex_;
+  size_t num_collapses_;
+
+ public:
+  typedef typename SkBlComplex::Vertex_handle Vertex_handle;
+  typedef typename SkBlComplex::Edge_handle Edge_handle;
+
+  /**
+   * @brief Modify complex to be the expansion of the k-nearest neighbor
+   * symetric graph.
+   */
+  Vertex_collapsor(SkBlComplex& complex, size_t num_collapses) :
+      complex_(complex), num_collapses_(num_collapses) {
+    // std::list<Vertex_handle> vertices;
+    // vertices.insert(vertices.begin(),complex_.vertex_range().begin(),complex_.vertex_range().end());
+    // UIDBG("Collapse vertices");
+    // collapse_vertices(vertices);
+
+    std::list<Vertex_handle> vertices;
+
+    UIDBG("Compute eps net");
+    Furthest_point_epsilon_net<Complex> eps_net(complex_);
+
+    for (auto vh : eps_net.net_filtration_)
+      vertices.push_back(vh.vertex_handle);
+
+    UIDBG("Collapse vertices");
+    collapse_vertices(vertices);
+  }
+
+ private:
+  void collapse_vertices(std::list<Vertex_handle>& vertices) {
+    while (!vertices.empty() && num_collapses_--) {
+      Vertex_handle current_vertex = vertices.front();
+      vertices.pop_front();
+      if (is_link_reducible(current_vertex))
+        complex_.remove_vertex(current_vertex);
+    }
+  }
+
+  bool is_link_reducible(Vertex_handle v) {
+    auto link = complex_.link(v);
+    if (link.empty()) return false;
+    if (link.is_cone()) return true;
+    if (link.num_connected_components() > 1) return false;
+    Edge_contractor<Complex> contractor(link, link.num_vertices() - 1);
+    return (link.num_vertices() == 1);
+  }
+};
+
+#endif  // UTILS_VERTEX_COLLAPSOR_H_
-- 
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