78 lines
2.0 KiB
C++
78 lines
2.0 KiB
C++
/*
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* Tensor3.h
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* @brief Rank 3 tensors based on http://www.gps.caltech.edu/~walter/FTensor/FTensor.pdf
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* Created on: Feb 10, 2010
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* @author: Frank Dellaert
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*/
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#pragma once
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#include "tensors.h"
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namespace tensors {
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/** Rank 3 Tensor */
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template<int N1, int N2, int N3>
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class Tensor3 {
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Tensor2<N1, N2> T[N3];
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public:
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/** default constructor */
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Tensor3() {
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}
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/** construct from data */
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Tensor3(const double data[N3][N2][N1]) {
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for (int k = 0; k < N3; k++)
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T[k] = data[k];
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}
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/** construct from expression */
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template<class A, char I, char J, char K>
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Tensor3(const Tensor3Expression<A, Index<N1, I> , Index<N2, J> , Index<N3,
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K> >& a) {
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for (int k = 0; k < N3; k++)
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T[k] = a(k);
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}
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double operator()(int i, int j, int k) const {
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return T[k](i, j);
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}
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/** convert to expression */
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template<char I, char J, char K> Tensor3Expression<Tensor3, Index<N1, I> ,
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Index<N2, J> , Index<N3, K> > operator()(const Index<N1, I>& i,
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const Index<N2, J>& j, const Index<N3, K>& k) {
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return Tensor3Expression<Tensor3, Index<N1, I> , Index<N2, J> , Index<N3,
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K> > (*this);
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}
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/** convert to expression */
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template<char I, char J, char K> Tensor3Expression<const Tensor3, Index<N1, I> ,
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Index<N2, J> , Index<N3, K> > operator()(const Index<N1, I>& i,
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const Index<N2, J>& j, const Index<N3, K>& k) const {
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return Tensor3Expression<const Tensor3, Index<N1, I> , Index<N2, J> , Index<N3,
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K> > (*this);
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}
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}; // Tensor3
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/** Rank 3 permutation tensor */
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struct Eta3 {
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/** calculate value. TODO: wasteful to actually use this */
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double operator()(int i, int j, int k) const {
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return ((j - i) * (k - i) * (k - j)) / 2;
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}
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/** create expression */
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template<char I, char J, char K> Tensor3Expression<Eta3, Index<3, I> ,
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Index<3, J> , Index<3, K> > operator()(const Index<3, I>& i,
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const Index<3, J>& j, const Index<3, K>& k) const {
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return Tensor3Expression<Eta3, Index<3, I> , Index<3, J> , Index<3, K> > (
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*this);
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}
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}; // Eta
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} // namespace tensors
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