78 lines
2.2 KiB
C++
78 lines
2.2 KiB
C++
// This file is part of libigl, a simple c++ geometry processing library.
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//
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// Copyright (C) 2015 Olga Diamanti, Alec Jacobson
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//
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// This Source Code Form is subject to the terms of the Mozilla Public License
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// v. 2.0. If a copy of the MPL was not distributed with this file, You can
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// obtain one at http://mozilla.org/MPL/2.0/.
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#include "nchoosek.h"
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#include <cmath>
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#include <cassert>
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IGL_INLINE double igl::nchoosek(const int n, const int k)
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{
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if(k>n/2)
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{
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return nchoosek(n,n-k);
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}else if(k==1)
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{
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return n;
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}else
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{
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double c = 1;
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for(int i = 1;i<=k;i++)
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{
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c *= (((double)n-k+i)/((double)i));
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}
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return std::round(c);
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}
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}
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template < typename DerivedV, typename DerivedU>
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IGL_INLINE void igl::nchoosek(
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const Eigen::MatrixBase<DerivedV> & V,
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const int k,
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Eigen::PlainObjectBase<DerivedU> & U)
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{
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using namespace Eigen;
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if(V.size() == 0)
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{
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U.resize(0,k);
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return;
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}
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assert((V.cols() == 1 || V.rows() == 1) && "V must be a vector");
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U.resize(nchoosek(V.size(),k),k);
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int running_i = 0;
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int running_j = 0;
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Matrix<typename DerivedU::Scalar,1,Dynamic> running(1,k);
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int N = V.size();
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const std::function<void(int,int)> doCombs =
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[&running,&N,&doCombs,&running_i,&running_j,&U,&V](int offset, int k)
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{
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if(k==0)
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{
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U.row(running_i) = running;
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running_i++;
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return;
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}
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for (int i = offset; i <= N - k; ++i)
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{
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running(running_j) = V(i);
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running_j++;
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doCombs(i+1,k-1);
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running_j--;
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}
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};
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doCombs(0,k);
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}
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#ifdef IGL_STATIC_LIBRARY
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// Explicit template instantiation
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template void igl::nchoosek<Eigen::Matrix<int, -1, 1, 0, -1, 1>, Eigen::Matrix<int, -1, -1, 0, -1, -1> >(Eigen::MatrixBase<Eigen::Matrix<int, -1, 1, 0, -1, 1> > const&, int, Eigen::PlainObjectBase<Eigen::Matrix<int, -1, -1, 0, -1, -1> >&);
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#if EIGEN_VERSION_AT_LEAST(3,3,0)
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#else
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template void igl::nchoosek<Eigen::CwiseNullaryOp<Eigen::internal::linspaced_op<int, true>, Eigen::Matrix<int, -1, 1, 0, -1, 1> >, Eigen::Matrix<int, -1, -1, 0, -1, -1> >(Eigen::MatrixBase<Eigen::CwiseNullaryOp<Eigen::internal::linspaced_op<int, true>, Eigen::Matrix<int, -1, 1, 0, -1, 1> > > const&, int, Eigen::PlainObjectBase<Eigen::Matrix<int, -1, -1, 0, -1, -1> >&);
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#endif
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#endif
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