DirectAccessWithHoles.cpp

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/** @example DirectAccessWithHoles.cpp \n
 * \brief Use direct access to MOAB data to avoid calling through API \n
 *
 * This example creates a 1d row of quad elements, with a user-specified number of "holes" (missing
 * quads) in the row: \verbatim
 * ---------------------- ---------------------- --------
 * | | | | | | | | | |
 * | | | |(hole)| | | |(hole)| | ...
 * | | | | | | | | | |
 * ---------------------- ---------------------- --------
 * \endverbatim
 * This makes (nholes+1) contiguous runs of quad handles in the handle space
 * This example shows how to use the xxx_iterate functions in MOAB (xxx = coords, connect, tag,
 * adjacencies) to get direct pointer access to MOAB internal storage, which can be used without
 * calling through the MOAB API.
 *
 * -# Initialize MOAB \n
 * -# Create a quad mesh with holes, 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
 * -# Set up map from starting quad handle for a chunk to struct of (tag1_ptr, tag2_ptr,
 * tag3_ptr), pointers to the dense tag storage for those tags for the chunk
 * -# 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 DirectAccessWithHoles \n
 * <b>To run</b>: ./DirectAccess [-nquads <# quads>] [-holes <# holes>]\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_with_holes( Interface* mbImpl, int nquads, int nholes );
 
struct tag_struct
{
 double* avg_ptr;
 int* nv_ptr;
};
 
int main( int argc, char** argv )
{
 // Get MOAB instance
 Interface* mbImpl = new( std::nothrow ) Core;
 if( NULL == mbImpl ) return 1;
 
 int nquads = 1000, nholes = 1;
 
 // Parse options
 ProgOptions opts;
 opts.addOpt< int >( string( "nquads,n" ), string( "Number of quads in the mesh (default = 1000" ), &nquads );
 opts.addOpt< int >( string( "holes,H" ), string( "Number of holes in the element handle space (default = 1" ),
 &nholes );
 opts.parseCommandLine( argc, argv );
 if( nholes >= nquads )
 {
 cerr << "Number of holes needs to be < number of elements." << endl;
 return 1;
 }
 
 // Create simple structured mesh with hole, but using unstructured representation
 ErrorCode rval = create_mesh_with_holes( mbImpl, nquads, nholes );MB_CHK_SET_ERR( rval, "Trouble creating mesh" );
 
 // Get all vertices and non-vertex entities
 Range verts, elems;
 rval = mbImpl->get_entities_by_handle( 0, elems );MB_CHK_SET_ERR( rval, "Trouble getting all entities" );
 verts = elems.subset_by_dimension( 0 );
 elems -= 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 connectivity, coordinate, tag, and adjacency iterators
 EntityHandle* conn_ptr;
 double *x_ptr, *y_ptr, *z_ptr, *tag1_ptr, *tag2_ptr;
 int* tag3_ptr;
 
 // First vertex is at start of range (ranges are sorted), and is offset for vertex index
 // calculation
 EntityHandle first_vert = *verts.begin();
 
 // When iterating over elements, each chunk can have a different # vertices; also, count tells
 // you how many elements are in the current chunk
 int vpere, count;
 
 // Get coordinates iterator, just need this once because we know verts handle space doesn't have
 // holes
 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
 
 // Iterate through elements, computing midpoint based on vertex positions, set on element-based
 // tag1 Control loop by iterator over elem range
 Range::iterator e_it = elems.begin();
 
 while( e_it != elems.end() )
 {
 // Get conn_ptr, tag1_ptr for next contiguous chunk of element handles, and coords pointers
 // for all verts
 rval = mbImpl->connect_iterate( e_it, elems.end(), conn_ptr, vpere, count );MB_CHK_SET_ERR( rval, "Error in connect_iterate" );
 rval = mbImpl->tag_iterate( tag1, e_it, elems.end(), count, (void*&)tag1_ptr );MB_CHK_SET_ERR( rval, "Error in tag1_iterate" );
 
 // Iterate over elements in this chunk
 for( int i = 0; i < count; i++ )
 {
 tag1_ptr[0] = tag1_ptr[1] = tag1_ptr[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[j] - first_vert; // vert index is just the offset from first vertex
 tag1_ptr[0] += x_ptr[v_index];
 tag1_ptr[1] += y_ptr[v_index]; // Sum vertex positions into tag1...
 tag1_ptr[2] += z_ptr[v_index];
 }
 tag1_ptr[0] /= vpere;
 tag1_ptr[1] /= vpere; // Then normalize
 tag1_ptr[2] /= vpere;
 
 // Done with this element; advance connect_ptr and tag1_ptr to next element
 conn_ptr += vpere;
 tag1_ptr += 3;
 } // Loop over elements in chunk
 
 // Done with chunk; advance range iterator by count; will skip over gaps in range
 e_it += count;
 } // While loop over all elements
 
 // Iterate through vertices, summing positions into tag2 on connected elements and incrementing
 // vertex count Iterate over chunks the same as elements, even though we know we have only one
 // chunk here, just to show how it's done
 
 // Create a std::map from EntityHandle (first entity handle in chunk) to
 // tag_struct (ptrs to start of avg/#verts tags for that chunk); then for a given entity handle,
 // we can quickly find the chunk it's in using map::lower_bound; could have set up this map in
 // earlier loop over elements, but do it here for clarity
 
 map< EntityHandle, tag_struct > elem_map;
 e_it = elems.begin();
 while( e_it != elems.end() )
 {
 tag_struct ts = { NULL, NULL };
 rval = mbImpl->tag_iterate( tag2, e_it, elems.end(), count, (void*&)ts.avg_ptr );MB_CHK_SET_ERR( rval, "Error in tag2_iterate" );
 rval = mbImpl->tag_iterate( tag3, e_it, elems.end(), count, (void*&)ts.nv_ptr );MB_CHK_SET_ERR( rval, "Error in tag3_iterate" );
 elem_map[*e_it] = ts;
 e_it += count;
 }
 
 // Call a vertex-quad adjacencies function to generate vertex-element adjacencies in MOAB
 Range::iterator v_it = verts.begin();
 Range dum_range;
 rval = mbImpl->get_adjacencies( &( *v_it ), 1, 2, false, dum_range );MB_CHK_SET_ERR( rval, "Error in get_adjacencies" );
 const vector< EntityHandle >** adjs_ptr;
 while( v_it != verts.end() )
 {
 // Get coords ptrs, adjs_ptr; can't set tag2_ptr by direct access, because of hole in
 // element handle space
 rval = mbImpl->coords_iterate( v_it, verts.end(), x_ptr, y_ptr, z_ptr, count );MB_CHK_SET_ERR( rval, "Error in coords_iterate" );
 rval = mbImpl->adjacencies_iterate( v_it, verts.end(), adjs_ptr, count );MB_CHK_SET_ERR( rval, "Error in adjacencies_iterate" );
 
 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 )
 {
 // Get chunk that this element resides in; upper_bound points to the first element
 // strictly > key, so get that and decrement (would work the same as lower_bound
 // with an if-test and decrement)
 map< EntityHandle, tag_struct >::iterator mit = elem_map.upper_bound( *ait );
 --mit;
 // Index of *ait in that chunk
 int a_ind = *ait - ( *mit ).first;
 tag_struct ts = ( *mit ).second;
 ts.avg_ptr[3 * a_ind + 0] += x_ptr[v]; // Tag on each element is 3 doubles, x/y/z
 ts.avg_ptr[3 * a_ind + 1] += y_ptr[v];
 ts.avg_ptr[3 * a_ind + 2] += z_ptr[v];
 ts.nv_ptr[a_ind]++; // Increment the vertex count
 }
 }
 
 v_it += count;
 }
 
 // Normalize tag2 by vertex count; loop over elements using same approach as before
 // At the same time, compare values of tag1 and tag2
 e_it = elems.begin();
 while( e_it != elems.end() )
 {
 // Get conn_ptr, tag1_ptr for next contiguous chunk of element handles, and coords pointers
 // for all verts
 rval = mbImpl->tag_iterate( tag1, e_it, elems.end(), count, (void*&)tag1_ptr );MB_CHK_SET_ERR( rval, "Error in tag1_iterate" );
 rval = mbImpl->tag_iterate( tag2, e_it, elems.end(), count, (void*&)tag2_ptr );MB_CHK_SET_ERR( rval, "Error in tag2_iterate" );
 rval = mbImpl->tag_iterate( tag3, e_it, elems.end(), count, (void*&)tag3_ptr );MB_CHK_SET_ERR( rval, "Error in tag3_iterate" );
 
 // Iterate over elements in this chunk
 for( int i = 0; i < count; i++ )
 {
 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 " << *e_it + i << endl;
 }
 
 e_it += count;
 }
 
 // Ok, we're done, shut down MOAB
 delete mbImpl;
 
 return 0;
}
 
ErrorCode create_mesh_with_holes( Interface* mbImpl, int nquads, int nholes )
{
 // 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 4(nquads+1) because they're in a 1d row; will initialize coords in loop
 // over elems 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 elems
 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;
 for( int j = 0; j < 4; j++ )
 connect[4 * i + j] = quad_v + j; // Connectivity of each quad is a sequence starting from quad_v
 }
 // 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)
 
 // Now delete nholes elements, spaced approximately equally through mesh, so contiguous size is
 // about nquads/(nholes + 1) reinterpret start_elem as the next element to be deleted
 int de = nquads / ( nholes + 1 );
 for( int i = 0; i < nholes; i++ )
 {
 start_elem += de;
 rval = mbImpl->delete_entities( &start_elem, 1 );MB_CHK_SET_ERR( rval, "Error in delete_entities" );
 }
 
 return MB_SUCCESS;
}