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.
This example :

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):
1. Get the element corresponding to (i,j,k)
2. Get the connectivity of the element
3. Get the coordinates of the vertices comprising that element
Release the structured mesh interface and destroy the MOAB instance

To run: ./StructuredMeshSimple [d [N] ]
(default values so can run w/ no user interaction)

/** @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;
}