improve_partition.cc

#include <cassert>
#include <memory>
#include <vector>
#include <iostream>
#include <thread>

#include <mtkahypar.h>

// Install library interface via 'sudo make install.mtkahypar' in build folder
// Compile with: g++ -std=c++14 -DNDEBUG -O3 improve_partition.cc -o example -lmtkahypar
int main(int argc, char* argv[]) {
  mt_kahypar_error_t error{};

  // Initialize thread pool
  mt_kahypar_initialize(
    std::thread::hardware_concurrency() /* use all available cores */,
    true /* activate interleaved NUMA allocation policy */ );

  // Setup partitioning context
  mt_kahypar_context_t* context = mt_kahypar_context_from_preset(DEFAULT);
  // In the following, we partition a hypergraph into eight blocks
  // with an allowed imbalance of 3% and optimize the connective metric (KM1)
  mt_kahypar_set_partitioning_parameters(context,
    8 /* number of blocks */, 0.03 /* imbalance parameter */,
    KM1 /* objective function */);
  mt_kahypar_set_seed(42 /* seed */);
  // Enable logging
  mt_kahypar_status_t status =
    mt_kahypar_set_context_parameter(context, VERBOSE, "1", &error);
  assert(status == SUCCESS);

 // Load Hypergraph for DEFAULT preset
  mt_kahypar_hypergraph_t hypergraph =
    mt_kahypar_read_hypergraph_from_file("ibm01.hgr",
      context, HMETIS /* file format */, &error);
  if (hypergraph.hypergraph == nullptr) {
    std::cout << error.msg << std::endl; std::exit(1);
  }

  // Read Partition File, which we improve with the QUALITY preset
  mt_kahypar_context_t* context_quality = mt_kahypar_context_from_preset(QUALITY);
  mt_kahypar_set_partitioning_parameters(context_quality, 8, 0.03, KM1);
  status = mt_kahypar_set_context_parameter(context_quality, VERBOSE, "1", &error);
  assert(status == SUCCESS);

  mt_kahypar_partitioned_hypergraph_t partitioned_hg =
    mt_kahypar_read_partition_from_file(
      hypergraph, context_quality, 8 /* number of blocks */, "ibm01.hgr.part8", &error);
  if (partitioned_hg.partitioned_hg == nullptr) {
    std::cout << error.msg << std::endl; std::exit(1);
  }

  // Improve Partition
  const int km1_before = mt_kahypar_km1(partitioned_hg);
  mt_kahypar_improve_partition(partitioned_hg, context_quality,
    1 /* perform one multilevel improvement cycle (also called V-cycle) */, &error);
  const int km1_after = mt_kahypar_km1(partitioned_hg);

  // Output Results
  std::cout << "Partitioning Results:" << std::endl;
  std::cout << "Km1 before Improvement Cycle = " << km1_before << std::endl;
  std::cout << "Km1 after Improvement Cycle  = " << km1_after << std::endl;

  mt_kahypar_free_context(context);
  mt_kahypar_free_context(context_quality);
  mt_kahypar_free_hypergraph(hypergraph);
  mt_kahypar_free_partitioned_hypergraph(partitioned_hg);
}