StructuredMeshSimple.cpp

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/** @example StructuredMeshSimple.cpp
 * \brief Show creation and query of structured mesh, serial or parallel, through MOAB's structured
 * mesh interface. This is an example showing creation and query of a 3D structured mesh.  In
 * serial, a single N*N*N block of elements is created; in parallel, each proc gets an N*N*N block,
 * with blocks arranged in a 1d column, sharing vertices and faces at their interfaces (proc 0 has
 * no left neighbor and proc P-1 no right neighbor). Each square block of hex elements is then
 * referenced by its ijk parameterization. 1D and 2D examples could be made simply by changing the
 * dimension parameter passed into the MOAB functions. \n
 *
 * <b>This example </b>:
 *    -# Instantiate MOAB and get the structured mesh interface
 *    -# Decide what the local parameters of the mesh will be, based on parallel/serial and rank.
 *    -# Create a N^d structured mesh, which includes (N+1)^d vertices and N^d elements.
 *    -# Get the vertices and elements from moab and check their numbers against (N+1)^d and N^d,
 * resp.
 *    -# Loop over elements in d nested loops over i, j, k; for each (i,j,k):
 *      -# Get the element corresponding to (i,j,k)
 *      -# Get the connectivity of the element
 *      -# Get the coordinates of the vertices comprising that element
 *    -# Release the structured mesh interface and destroy the MOAB instance
 *
 * <b> To run: </b> ./StructuredMeshSimple [d [N] ] \n
 * (default values so can run w/ no user interaction)
 */

#include "moab/Core.hpp"
#include "moab/ScdInterface.hpp"
#include "moab/ProgOptions.hpp"
#include "moab/CN.hpp"
#ifdef MOAB_HAVE_MPI
#include "moab_mpi.h"
#endif
#include <iostream>
#include <vector>

using namespace moab;
using namespace std;

int main( int argc, char** argv )
{
    int N = 10, dim = 3;

#ifdef MOAB_HAVE_MPI
    MPI_Init( &argc, &argv );
#endif

    ProgOptions opts;
    opts.addOpt< int >( string( "dim,d" ), string( "Dimension of mesh (default=3)" ), &dim );
    opts.addOpt< int >( string( ",n" ), string( "Number of elements on a side (default=10)" ), &N );
    opts.parseCommandLine( argc, argv );

    // 0. Instantiate MOAB and get the structured mesh interface
    Interface* mb = new( std::nothrow ) Core;
    if( NULL == mb ) return 1;
    ScdInterface* scdiface;
    ErrorCode rval = mb->query_interface( scdiface );MB_CHK_ERR( rval );  // Get a ScdInterface object through moab instance

    // 1. Decide what the local parameters of the mesh will be, based on parallel/serial and rank.
#ifdef MOAB_HAVE_MPI
    int rank = 0, nprocs = 1;
    MPI_Comm_size( MPI_COMM_WORLD, &nprocs );
    MPI_Comm_rank( MPI_COMM_WORLD, &rank );
    int ilow = rank * N, ihigh = ilow + N;
#else
    int rank = 0;
    int ilow = 0, ihigh = N;
#endif

    // 2. Create a N^d structured mesh, which includes (N+1)^d vertices and N^d elements.
    ScdBox* box;
    rval = scdiface->construct_box(
        HomCoord( ilow, ( dim > 1 ? 0 : -1 ),
                  ( dim > 2 ? 0 : -1 ) ),  // Use in-line logical tests to handle dimensionality
        HomCoord( ihigh, ( dim > 1 ? N : -1 ), ( dim > 2 ? N : -1 ) ), NULL,
        0,  // NULL coords vector and 0 coords (don't specify coords for now)
        box );MB_CHK_ERR( rval );  // box is the structured box object providing the parametric
                         // structured mesh interface for this rectangle of elements

    // 3. Get the vertices and elements from moab and check their numbers against (N+1)^d and N^d,
    // resp.
    Range verts, elems;
    rval = mb->get_entities_by_dimension( 0, 0, verts );MB_CHK_ERR( rval );  // First '0' specifies "root set", or entire MOAB instance, second the
    // entity dimension being requested
    rval = mb->get_entities_by_dimension( 0, dim, elems );MB_CHK_ERR( rval );

#define MYSTREAM( a ) \
    if( !rank ) cout << ( a ) << endl

    if( pow( N, dim ) == (int)elems.size() && pow( N + 1, dim ) == (int)verts.size() )
    {  // Expected #e and #v are N^d and (N+1)^d, resp.
#ifdef MOAB_HAVE_MPI
        MYSTREAM( "Proc 0: " );
#endif
        MYSTREAM( "Created " << elems.size() << " " << CN::EntityTypeName( mb->type_from_handle( *elems.begin() ) )
                             << " elements and " << verts.size() << " vertices." << endl );
    }
    else
        cout << "Created the wrong number of vertices or hexes!" << endl;

    // 4. Loop over elements in 3 nested loops over i, j, k; for each (i,j,k):
    vector< double > coords( 3 * pow( N + 1, dim ) );
    vector< EntityHandle > connect;
    for( int k = 0; k < ( dim > 2 ? N : 1 ); k++ )
    {
        for( int j = 0; j < ( dim > 1 ? N : 1 ); j++ )
        {
            for( int i = 0; i < N - 1; i++ )
            {
                // 4a. Get the element corresponding to (i,j,k)
                EntityHandle ehandle = box->get_element( i, j, k );
                if( 0 == ehandle ) return MB_FAILURE;
                // 4b. Get the connectivity of the element
                rval = mb->get_connectivity( &ehandle, 1, connect );MB_CHK_ERR( rval );  // Get the connectivity, in canonical order
                // 4c. Get the coordinates of the vertices comprising that element
                rval = mb->get_coords( &connect[0], connect.size(), &coords[0] );MB_CHK_ERR( rval );  // Get the coordinates of those vertices
            }
        }
    }

    // 5. Release the structured mesh interface and destroy the MOAB instance
    mb->release_interface( scdiface );  // Tell MOAB we're done with the ScdInterface

#ifdef MOAB_HAVE_MPI
    MPI_Finalize();
#endif

    return 0;
}