docs/moab/DirectAccessNoHoles_8cpp-example.html

/** @example DirectAccessNoHoles.cpp \n

 * \brief Use direct access to MOAB data to avoid calling through API \n

 *

 * This example creates a 1d row of quad elements, such that all quad and vertex handles

 * are contiguous in the handle space and in the database.  Then it shows how to get access

 * to pointers to MOAB-native data for vertex coordinates, quad connectivity, tag storage,

 * and vertex to quad adjacency lists.  This allows applications to access this data directly

 * without going through MOAB's API.  In cases where the mesh is not changing (or only mesh

 * vertices are moving), this can save significant execution time in applications.

 * \verbatim

 *  ----------------------

 *  |      |      |      |

 *  |      |      |      | ...

 *  |      |      |      |

 *  ----------------------

 * \endverbatim

 *    -#  Initialize MOAB \n

 *    -#  Create a quad mesh, as depicted above

 *    -#  Create 2 dense tags (tag1, tag2) for avg position to assign to quads, and # verts per quad

 * (tag3)

 *    -#  Get connectivity, coordinate, tag1 iterators

 *    -#  Iterate through quads, computing midpoint based on vertex positions, set on quad-based

 * tag1

 *    -#  Iterate through vertices, summing positions into tag2 on connected quads and incrementing

 * vertex count

 *    -#  Iterate through quads, normalizing tag2 by vertex count and comparing values of tag1 and

 * tag2

 *

 * <b>To compile</b>: \n

 *    make DirectAccessNoHoles \n

 * <b>To run</b>: ./DirectAccessNoHoles [-nquads <# quads>]\n

 *

 */


#include "moab/Core.hpp"

#include "moab/ProgOptions.hpp"

#include "moab/ReadUtilIface.hpp"

#include <map>

#include <iostream>

#include <cassert>


using namespace moab;

using namespace std;


ErrorCode create_mesh_no_holes( Interface* mbImpl, int nquads );


int main( int argc, char** argv )

{

    // Get MOAB instance

    Interface* mbImpl = new( std::nothrow ) Core;

    if( NULL == mbImpl ) return 1;


    int nquads = 1000;


    // Parse options

    ProgOptions opts;

    opts.addOpt< int >( string( "nquads,n" ), string( "Number of quads in the mesh (default = 1000" ), &nquads );

    opts.parseCommandLine( argc, argv );


    // Create simple structured mesh with hole, but using unstructured representation

    ErrorCode rval = create_mesh_no_holes( mbImpl, nquads );MB_CHK_SET_ERR( rval, "Trouble creating mesh" );


    // Get all vertices and non-vertex entities

    Range verts, quads;

    rval = mbImpl->get_entities_by_handle( 0, quads );MB_CHK_SET_ERR( rval, "Trouble getting all entities" );

    verts = quads.subset_by_dimension( 0 );

    quads -= verts;


    // Create tag1 (element-based avg), tag2 (vertex-based avg), tag3 (# connected verts)

    Tag tag1, tag2, tag3;

    rval = mbImpl->tag_get_handle( "tag1", 3, MB_TYPE_DOUBLE, tag1, MB_TAG_DENSE | MB_TAG_CREAT );MB_CHK_SET_ERR( rval, "Trouble creating tag1" );

    double def_val[3] = { 0.0, 0.0, 0.0 };  // need a default value for tag2 because we sum into it

    rval              = mbImpl->tag_get_handle( "tag2", 3, MB_TYPE_DOUBLE, tag2, MB_TAG_DENSE | MB_TAG_CREAT, def_val );MB_CHK_SET_ERR( rval, "Trouble creating tag2" );

    int def_val_int = 0;  // need a default value for tag3 because we increment it

    rval = mbImpl->tag_get_handle( "tag3", 1, MB_TYPE_INTEGER, tag3, MB_TAG_DENSE | MB_TAG_CREAT, &def_val_int );MB_CHK_SET_ERR( rval, "Trouble creating tag3" );


    // Get pointers to connectivity, coordinate, tag, and adjacency arrays; each of these returns a

    // count, which should be compared to the # entities you expect to verify there's only one chunk

    // (no holes)

    int count, vpere;

    EntityHandle* conn_ptr;

    rval = mbImpl->connect_iterate( quads.begin(), quads.end(), conn_ptr, vpere, count );MB_CHK_SET_ERR( rval, "Error in connect_iterate" );

    assert( count == (int)quads.size() );  // Should end up with just one contiguous chunk of quads


    double *x_ptr, *y_ptr, *z_ptr;

    rval = mbImpl->coords_iterate( verts.begin(), verts.end(), x_ptr, y_ptr, z_ptr, count );MB_CHK_SET_ERR( rval, "Error in coords_iterate" );

    assert( count == (int)verts.size() );  // Should end up with just one contiguous chunk of vertices


    double *tag1_ptr, *tag2_ptr;

    int* tag3_ptr;

    rval = mbImpl->tag_iterate( tag1, quads.begin(), quads.end(), count, (void*&)tag1_ptr );MB_CHK_SET_ERR( rval, "Error in tag1_iterate" );

    assert( count == (int)quads.size() );  // Should end up with just one contiguous chunk of quads

    rval = mbImpl->tag_iterate( tag2, quads.begin(), quads.end(), count, (void*&)tag2_ptr );MB_CHK_SET_ERR( rval, "Error in tag2_iterate" );

    assert( count == (int)quads.size() );  // Should end up with just one contiguous chunk of quads

    rval = mbImpl->tag_iterate( tag3, quads.begin(), quads.end(), count, (void*&)tag3_ptr );MB_CHK_SET_ERR( rval, "Error in tag3_iterate" );

    assert( count == (int)quads.size() );  // Should end up with just one contiguous chunk of quads


    const vector< EntityHandle >** adjs_ptr;

    rval = mbImpl->adjacencies_iterate( verts.begin(), verts.end(), adjs_ptr, count );MB_CHK_SET_ERR( rval, "Error in adjacencies_iterate" );

    assert( count == (int)verts.size() );  // Should end up with just one contiguous chunk of vertices

    // Start_ handles used to compute indices into vertex/quad arrays; can use direct subtraction

    // because we know there aren't any holes in the handle spaces for verts or quads

    EntityHandle start_vert = *verts.begin(), start_quad = *quads.begin();


    // Iterate over elements, computing tag1 from coords positions

    for( int i = 0; i < nquads; i++ )

    {

        tag1_ptr[3 * i + 0] = tag1_ptr[3 * i + 1] = tag1_ptr[3 * i + 2] = 0.0;  // Initialize position for this element

        for( int j = 0; j < vpere; j++ )

        {                                                        // Loop over vertices in this element

            int v_index = conn_ptr[vpere * i + j] - start_vert;  // vert index is just the offset from start vertex

            tag1_ptr[3 * i + 0] += x_ptr[v_index];

            tag1_ptr[3 * i + 1] += y_ptr[v_index];  // Sum vertex positions into tag1...

            tag1_ptr[3 * i + 2] += z_ptr[v_index];

        }

        tag1_ptr[3 * i + 0] /= vpere;

        tag1_ptr[3 * i + 1] /= vpere;  // Then normalize

        tag1_ptr[3 * i + 2] /= vpere;

    }  // Loop over elements in chunk


    // Iterate through vertices, summing positions into tag2 on connected elements and incrementing

    // vertex count

    for( int v = 0; v < count; v++ )

    {

        const vector< EntityHandle >* avec = *( adjs_ptr + v );

        for( vector< EntityHandle >::const_iterator ait = avec->begin(); ait != avec->end(); ++ait )

        {

            // *ait is the quad handle, its index is computed by subtracting the start quad handle

            int a_ind = *ait - start_quad;

            tag2_ptr[3 * a_ind + 0] += x_ptr[v];  // Tag on each element is 3 doubles, x/y/z

            tag2_ptr[3 * a_ind + 1] += y_ptr[v];

            tag2_ptr[3 * a_ind + 2] += z_ptr[v];

            tag3_ptr[a_ind]++;  // Increment the vertex count

        }

    }


    // Normalize tag2 by vertex count (tag3); loop over elements using same approach as before

    // At the same time, compare values of tag1 and tag2

    int n_dis = 0;

    for( Range::iterator q_it = quads.begin(); q_it != quads.end(); ++q_it )

    {

        int i = *q_it - start_quad;

        for( int j = 0; j < 3; j++ )

            tag2_ptr[3 * i + j] /= (double)tag3_ptr[i];  // Normalize by # verts

        if( tag1_ptr[3 * i] != tag2_ptr[3 * i] || tag1_ptr[3 * i + 1] != tag2_ptr[3 * i + 1] ||

            tag1_ptr[3 * i + 2] != tag2_ptr[3 * i + 2] )

        {

            cout << "Tag1, tag2 disagree for element " << *q_it + i << endl;

            n_dis++;

        }

    }

    if( !n_dis ) cout << "All tags agree, success!" << endl;


    // Ok, we're done, shut down MOAB

    delete mbImpl;


    return 0;

}


ErrorCode create_mesh_no_holes( Interface* mbImpl, int nquads )

{

    // First make the mesh, a 1d array of quads with left hand side x = elem_num; vertices are

    // numbered in layers

    ReadUtilIface* read_iface;

    ErrorCode rval = mbImpl->query_interface( read_iface );MB_CHK_SET_ERR( rval, "Error in query_interface" );

    vector< double* > coords;

    EntityHandle start_vert, start_elem, *connect;

    // Create verts, num is 2(nquads+1) because they're in a 1d row; will initialize coords in loop

    // over quads later

    rval = read_iface->get_node_coords( 3, 2 * ( nquads + 1 ), 0, start_vert, coords );MB_CHK_SET_ERR( rval, "Error in get_node_arrays" );

    // Create quads

    rval = read_iface->get_element_connect( nquads, 4, MBQUAD, 0, start_elem, connect );MB_CHK_SET_ERR( rval, "Error in get_element_connect" );

    for( int i = 0; i < nquads; i++ )

    {

        coords[0][2 * i] = coords[0][2 * i + 1] = (double)i;  // x values are all i

        coords[1][2 * i]                        = 0.0;

        coords[1][2 * i + 1]                    = 1.0;          // y coords

        coords[2][2 * i] = coords[2][2 * i + 1] = (double)0.0;  // z values, all zero (2d mesh)

        EntityHandle quad_v                     = start_vert + 2 * i;

        connect[4 * i + 0]                      = quad_v;

        connect[4 * i + 1]                      = quad_v + 2;

        connect[4 * i + 2]                      = quad_v + 3;

        connect[4 * i + 3]                      = quad_v + 1;

    }


    // Last two vertices

    // Cppcheck warning (false positive): variable coords is assigned a value that is never used

    coords[0][2 * nquads] = coords[0][2 * nquads + 1] = (double)nquads;

    coords[1][2 * nquads]                             = 0.0;

    coords[1][2 * nquads + 1]                         = 1.0;          // y coords

    coords[2][2 * nquads] = coords[2][2 * nquads + 1] = (double)0.0;  // z values, all zero (2d mesh)


    // Call a vertex-quad adjacencies function to generate vertex-element adjacencies in MOAB

    Range dum_range;

    rval = mbImpl->get_adjacencies( &start_vert, 1, 2, false, dum_range );MB_CHK_SET_ERR( rval, "Error in get_adjacencies" );

    assert( !dum_range.empty() );


    return MB_SUCCESS;

}