libigl_Martin/find.h

#ifndef IGL_FIND_H
#define IGL_FIND_H
#define EIGEN_YES_I_KNOW_SPARSE_MODULE_IS_NOT_STABLE_YET
#include <Eigen/Dense>
#include <Eigen/Sparse>
namespace igl
{
  // Find the non-zero entries and there respective indices in a sparse matrix.
  // Like matlab's [I,J,V] = find(X)
  //
  // Templates:
  //   T  should be a eigen sparse matrix primitive type like int or double
  // Input:
  //   X  m by n matrix whose entries are to be found 
  // Outputs:
  //   I  nnz vector of row indices of non zeros entries in X
  //   J  nnz vector of column indices of non zeros entries in X
  //   V  nnz vector of type T non-zeros entries in X
  //
  template <typename T>
  inline void find(
    const Eigen::SparseMatrix<T>& X,
    Eigen::Matrix<int,Eigen::Dynamic,1> & I,
    Eigen::Matrix<int,Eigen::Dynamic,1> & J,
    Eigen::Matrix<T,Eigen::Dynamic,1> & V);
  // Find the non-zero entries and there respective indices in a sparse vector.
  // Similar to matlab's [I,J,V] = find(X), but instead of [I,J] being
  // subscripts into X, since X is a vector we just return I, a list of indices
  // into X
  //
  // Templates:
  //   T  should be a eigen sparse matrix primitive type like int or double
  // Input:
  //   X  vector whose entries are to be found
  // Outputs:
  //   I  nnz vector of indices of non zeros entries in X
  //   V  nnz vector of type T non-zeros entries in X
  template <typename T>
  inline void find(
    const Eigen::SparseVector<T>& X,
    Eigen::Matrix<int,Eigen::Dynamic,1> & I,
    Eigen::Matrix<T,Eigen::Dynamic,1> & V);
}

// Implementation
#include "verbose.h"
  
template <typename T>
inline void igl::find(
  const Eigen::SparseMatrix<T>& X,
  Eigen::Matrix<int,Eigen::Dynamic,1> & I,
  Eigen::Matrix<int,Eigen::Dynamic,1> & J,
  Eigen::Matrix<T,Eigen::Dynamic,1> & V)
{
  // Resize outputs to fit nonzeros
  I.resize(X.nonZeros());
  J.resize(X.nonZeros());
  V.resize(X.nonZeros());

  int i = 0;
  // Iterate over outside
  for(int k=0; k<X.outerSize(); ++k)
  {
    // Iterate over inside
    for(typename Eigen::SparseMatrix<T>::InnerIterator it (X,k); it; ++it)
    {
      V(i) = it.value();
      I(i) = it.row();
      J(i) = it.col();
      i++;
    }
  }
}
  
template <typename T>
inline void igl::find(
  const Eigen::SparseVector<T>& X,
  Eigen::Matrix<int,Eigen::Dynamic,1> & I,
  Eigen::Matrix<T,Eigen::Dynamic,1> & V)
{
  // Resize outputs to fit nonzeros
  I.resize(X.nonZeros());
  V.resize(X.nonZeros());

  int i = 0;
  // loop over non-zeros
  for(typename Eigen::SparseVector<T>::InnerIterator it(X); it; ++it)
  {
    I(i) = it.index();
    V(i) = it.value();
    i++;
  }
}

#endif