Hierarchical compression

Available customizations

Compression via htool::HMatrixTreeBuilder can be customized in the following aspects:

1. For admissible condition, i.e., the geometric a priori we have to define admissible bloc, see Hierarchical clustering, the current strategy is:

   • htool::RjasanowSteinbach

2. For low-rank compression, see Low-rank compression, the available strategies are:

   • htool::SVD

   • htool::fullACA

   • htool::partialACA

   • htool::sympartialACA

   • htool::RecompressedLowRankGenerator

Strategies are then given to htool::HMatrixTreeBuilder via its constructor or its function members

1. htool::HMatrixTreeBuilder::set_admissibility_condition(),

2. htool::HMatrixTreeBuilder::set_low_rank_generator().

The constructor of htool::HMatrixTreeBuilder also takes the usual parameters for \(\mathcal{H}\)-matrix compression (tolerance for low-rank compression, symmetry, etc.), see its documentation.

Visualisation

Blocks from a htool::HMatrix can be exported to a file with htool::save_leaves_with_rank().

Information about compression can also but accessed from a htool::HMatrix with

• htool::get_tree_parameters(),

• htool::get_hmatrix_information(),

or directly exported to an output stream with

• htool::print_tree_parameters(),

• htool::print_hmatrix_information().