...one of the most highly
regarded and expertly designed C++ library projects in the
world.
— Herb Sutter and Andrei
Alexandrescu, C++
Coding Standards
namespace graph { namespace distributed { template<typename Graph, typename ComponentMap> typename property_traits<ComponentMap>::value_type connected_components_ps(const Graph& g, ComponentMap c) } }
The connected_components_ps() function computes the connected components of a graph by performing a breadth-first search from several sources in parallel while recording and eventually resolving the collisions.
<boost/graph/distributed/connected_components_parallel_search.hpp>
O(PN^2 + VNP) work, in O(N + V) time, where N is the number of mappings and V is the number of local vertices.
Every N th nodes starts a parallel search from the first vertex in their local vertex list during the first superstep (the other nodes remain idle during the first superstep to reduce the number of conflicts in numbering the components). At each superstep, all new component mappings from remote nodes are handled. If there is no work from remote updates, a new vertex is removed from the local list and added to the work queue.
Components are allocated from the component_value_allocator object, which ensures that a given component number is unique in the system, currently by using the rank and number of processes to stride allocations.
When two components are discovered to actually be the same component, a collision is recorded. The lower component number is prefered in the resolution, so component numbering resolution is consistent. After the search has exhausted all vertices in the graph, the mapping is shared with all processes and they independently resolve the comonent mapping. This phase can likely be significantly sped up if a clever algorithm for the reduction can be found.
Copyright (C) 2009 The Trustees of Indiana University.
Authors: Brian Barrett, Douglas Gregor, and Andrew Lumsdaine