void MathUtilities::extractLowerTriangularMatrix( const SparseMatrixsc& A, SparseMatrixsc& B )
{
std::vector< Eigen::Triplet<scalar> > triplets;
for( int col = 0; col < A.outerSize(); ++col )
{
for( SparseMatrixsc::InnerIterator it( A, col ); it; ++it )
{
if( col > it.row() ) { continue; }
triplets.push_back( Eigen::Triplet<scalar>( it.row(), col, it.value() ) );
}
}
B.resize( A.rows(), A.cols() );
B.setFromTriplets( triplets.begin(), triplets.end() );
B.makeCompressed();
}
void MathUtilities::convertDenseToSparse( const bool filter_zeros, const MatrixXXsc& dense_matrix, SparseMatrixsc& sparse_matrix )
{
std::vector<Eigen::Triplet<scalar>> triplets;
for( int row = 0; row < dense_matrix.rows(); ++row )
{
for( int col = 0; col < dense_matrix.cols(); ++col )
{
if( dense_matrix( row, col ) != 0.0 || !filter_zeros )
{
triplets.emplace_back( Eigen::Triplet<scalar>{ row, col, dense_matrix( row, col ) } );
}
}
}
sparse_matrix.resize( dense_matrix.rows(), dense_matrix.cols() );
sparse_matrix.setFromTriplets( std::begin( triplets ), std::end( triplets ) );
sparse_matrix.makeCompressed();
}
