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// This file is part of libigl, a simple c++ geometry processing library.
//
// Copyright (C) 2016 Michael Rabinovich <michaelrabinovich27@gmail.com>
// Copyright (C) 2017 Alec Jacobson <alecjacobson@gmail.com>
//
// This Source Code Form is subject to the terms of the Mozilla Public License
// v. 2.0. If a copy of the MPL was not distributed with this file, You can
// obtain one at http://mozilla.org/MPL/2.0/.
#ifndef IGL_EULER_CHARACTERISTIC_H
#define IGL_EULER_CHARACTERISTIC_H
#include "igl_inline.h"
#include <Eigen/Dense>
#include <Eigen/Sparse>
#include <vector>
namespace igl
{
/// Computes the Euler characteristic of a given mesh (V,F)
///
/// χ = |V| - |E| + |F|
///
/// For example,
/// - a single triangle has 3 - 3 + 1 = 1
/// - a tetrahedron has 4 - 6 + 4 = 2
///
/// @param[in] F #F by dim list of mesh faces (must be triangles)
/// @return An int containing the Euler characteristic
///
/// \note There is [some confusion](https://github.com/libigl/libigl/issues/2249#issue-1863608449) over the standard definition of Euler
/// characteristic. libigl's definition agrees with
/// [wikipedia](https://en.wikipedia.org/wiki/Euler_characteristic) and [David
/// Eppstein's
/// proofs](https://www.ics.uci.edu/~eppstein/junkyard/euler/all.html).
template <typename DerivedF>
IGL_INLINE int euler_characteristic(
const Eigen::MatrixBase<DerivedF> & F);
}
#ifndef IGL_STATIC_LIBRARY
# include "euler_characteristic.cpp"
#endif
#endif