ReadPartFile.cpp

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/** @example ReadPartFile.cpp
 * This example demonstrates how to read partition files created by Zoltan processes
 * and apply them to MOAB meshes. It shows how to:
 * - Load a mesh file and a partition file
 * - Remove existing partition sets from the mesh
 * - Create new partition sets based on the partition file
 * - Assign entities to appropriate partition sets
 * - Handle parallel partitioning with global IDs
 * - Write the partitioned mesh to a new file
 *
 * The partition file contains entity-to-partition assignments where entities
 * are identified by their global IDs. This is useful for load balancing
 * and parallel mesh processing workflows.
 *
 * Usage: ./ReadPartFile <input_mesh> <partition_file> <num_parts> <output_file>
 *
 * Example:
 * ./ReadPartFile mesh.h5m partition.txt 4 partitioned_mesh.h5m
 *
 * The partition file should contain one integer per entity (in order)
 * indicating which partition (0 to num_parts-1) each entity belongs to.
 */
 
#include "moab/Core.hpp"
#include <iostream>
#include <fstream>
#include <memory>
 
using namespace moab;
using namespace std;
 
#ifndef MESH_DIR
#define MESH_DIR "."
#endif
 
// Note: change the file name below to test a trivial "No such file or directory" error
string test_file_name = string( MESH_DIR ) + string( "/3k-tri-sphere.vtk" );
string part_file_name;
int nparts;
 
int main( int argc, char** argv )
{
    if( argc < 5 )
    {
        std::cerr << "Usage: " << argv[0] << " <input file> <part file> <#parts> <output file>\n";
        return 1;
    }
    std::string mesh_file = argv[1];
    std::string part_file = argv[2];
    int nparts            = std::stoi( argv[3] );
    std::string out_file  = argv[4];
 
    auto mb = std::make_unique< Core >();
    MB_CHK_SET_ERR( mb ? MB_SUCCESS : MB_FAILURE, "Error: Could not allocate MOAB Core instance." );
 
    std::ifstream inFile( part_file );
    MB_CHK_SET_ERR( inFile.is_open() ? MB_SUCCESS : MB_FAILURE, "Unable to open file " + part_file );
 
    MB_CHK_SET_ERR( mb->load_mesh( mesh_file.c_str() ), "Error: Could not load mesh file '" + mesh_file + "'" );
 
    Range sets;
    MB_CHK_SET_ERR( mb->get_entities_by_type( 0, MBENTITYSET, sets ), "Error: Could not get entity sets." );
    std::cout << "Number of sets is " << sets.size() << std::endl;
 
    Tag tag;
    MB_CHK_SET_ERR( mb->tag_get_handle( "PARALLEL_PARTITION", tag ), "Error: Could not get PARALLEL_PARTITION tag." );
 
    int num_deleted_sets = 0;
    for( auto it = sets.begin(); it != sets.end(); ++it )
    {
        EntityHandle eh = *it;
        int val         = -1;
        MB_CHK_SET_ERR( mb->tag_get_data( tag, &eh, 1, &val ), "Error: Unable to get tag data" );
        if( val != -1 )
        {
            num_deleted_sets++;
            MB_CHK_SET_ERR( mb->delete_entities( &eh, 1 ), "Error: Unable to delete entities" );
        }
    }
 
    if( num_deleted_sets )
        std::cout << "Deleted " << num_deleted_sets << " existing partition sets, and created new ones.\n";
 
    Range cells;
    MB_CHK_SET_ERR( mb->get_entities_by_dimension( 0, 2, cells ), "Error: Could not get dimension-2 entities." );
    std::vector< EntityHandle > psets( nparts );
    for( int i = 0; i < nparts; i++ )
    {
        MB_CHK_SET_ERR( mb->create_meshset( MESHSET_SET, psets[i] ), "Error: Could not create meshset." );
        MB_CHK_SET_ERR( mb->tag_set_data( tag, &( psets[i] ), 1, &i ), "Error: Could not set tag data." );
    }
 
    for( auto it = cells.begin(); it != cells.end(); ++it )
    {
        int part;
        EntityHandle eh = *it;
        inFile >> part;
        MB_CHK_SET_ERR( mb->add_entities( psets[part], &eh, 1 ), "Error: Could not add entity to partition set." );
    }
 
    MB_CHK_SET_ERR( mb->write_file( out_file.c_str() ), "Error: Could not write output mesh file '" + out_file + "'" );
    std::cout << "Partitioned mesh written to '" << out_file << "'.\n";
 
    return 0;
}