libigl/include/igl/slice_cached.h

// This file is part of libigl, a simple c++ geometry processing library.
// 
// Copyright (C) 2017 Daniele Panozzo <[email protected]>
// 
// 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_SLICE_CACHED_H
#define IGL_SLICE_CACHED_H
#include "igl_inline.h"
#define EIGEN_YES_I_KNOW_SPARSE_MODULE_IS_NOT_STABLE_YET
#include <Eigen/Dense>
#include <Eigen/Sparse>
namespace igl
{  

  /// Act like the matlab X(row_indices,col_indices) operator, where row_indices,
  /// col_indices are non-negative integer indices. This is a fast version of
  /// igl::slice that can analyze and store the sparsity structure. It is slower
  /// at the irst evaluation (slice_cached_precompute), but faster on the
  /// subsequent ones.
  /// 
  /// @param[in] X  m by n matrix
  /// @param[in] R  list of row indices
  /// @param[in] C  list of column indices
  /// @param[out] data Temporary data used by slice_cached to repeat this operation
  /// @param[out] Y  #R by #C matrix
  ///
  /// #### Example
  ///
  ///     // Construct and slice up Laplacian
  ///     Eigen::SparseMatrix<double> L,L_sliced;
  ///     igl::cotmatrix(V,F,L);
  ///     // Normal igl::slice call
  ///     igl::slice(L,in,in,L_in_in);
  ///     …
  ///     // Fast version
  ///     static Eigen::VectorXi data; // static or saved in a global state
  ///     if (data.size() == 0)
  ///       igl::slice_cached_precompute(L,in,in,data,L_sliced);
  ///     else
  ///       igl::slice_cached(L,data,L_sliced);
  ///
  /// \fileinfo
  template <typename TX, typename TY, typename DerivedI>
  IGL_INLINE void slice_cached_precompute(
    const Eigen::SparseMatrix<TX>& X,
    const Eigen::Matrix<int,Eigen::Dynamic,1> & R,
    const Eigen::Matrix<int,Eigen::Dynamic,1> & C,
    Eigen::MatrixBase<DerivedI>& data,
    Eigen::SparseMatrix<TY>& Y);
  /// Slice X by cached C,R indices into Y
  ///
  /// @param[in] X  m by n matrix
  /// @param[in] data Temporary data used by slice_cached to repeat this operation
  /// @param[out] Y  #R by #C matrix
  template <typename TX, typename TY, typename DerivedI>
  IGL_INLINE void slice_cached(
    const Eigen::SparseMatrix<TX>& X,
    const Eigen::MatrixBase<DerivedI>& data,
    Eigen::SparseMatrix<TY>& Y);
}

#ifndef IGL_STATIC_LIBRARY
#  include "slice_cached.cpp"
#endif

#endif