Hi Doug, All excellent points and I really hope it happens in some form :) . The BGL is great BUT yes usability should take more weight. My project manager was all for scrapping using the BGL because of some of these issues. I thought it was worth a couple more days graft to work out solutions because the payback using the BGL would be more than worth it. In my limited experience (2 months now) there are too many trip wires of the sort we are discussing. I got there in the end with my current problem but the axe is still hovering :( Can I add that misuse of graph assignment and a graph copy constructor is possible - corruptible shallow copies are the result. These methods should be given private scope to prevent (mis)use or be correctly implemented G2 = G1 ; // Compiles but NO you must use boost::graph_copy (G1, G2) instead
3) ... so long as we can still get maximal efficiency out of them when index maps are available.
This was exactly what I was asking in the original post, that my suggestion (in some form) be merged into the algorithm such that it is ONLY used if there is no vertex_index property available either by a graph vertex property OR a named parameter input to the algorithm.
4) ... that maintain vertex and edge index maps internally (as does the Python graph type).
I'm doing just this in a wrapper I have around the BGL graph types. So yes there is a problem that I guess others are also working around.
1) Make edge descriptors ordered (via <), so that users can make associative property maps more easily
Well guess what - I had to do this (but it won't work for multigraphs so it's not complete)! template<typename EdgeType> struct EdgeCompare : public std::binary_function<EdgeType, EdgeType, bool> { bool operator ()(const EdgeType& edge1, const EdgeType& edge2) const { if (edge1.m_source < edge2.m_source) return true ; if (edge1.m_source == edge2.m_source && edge1.m_target < edge2.m_target) return true ; return false ; } } ; /** An atom graph edge set type (i.e. a type that represents a set of atom/atom interactions) Note we need to supply a custom type containing a LessThanComparable functor to determine the sort order for AtomEdgeType */ typedef std::set<AtomEdgeType, EdgeCompare<AtomEdgeType> > AtomEdgeSetType ; Tony PS I've not introduced myself. I've worked on graph algorithms applications in computer chemical representation problems for 21 years and I am familiar with a whole range of graph algorithms for efficient graph isomorphism detection, subgraph isomorphism (Ullman, Sussenguth, Figeras etc), Morgan vertex labeling, graph partitioning (symmetry detection), maximal common subgraph, beta rings, k rings, smallest set of smallest rings (SSSR), extended SSSR etc etc. Hopefully over the next few years I'll be able to contribute new (to the BGL) algorithms if they prove useful. If I'm correct in my understanding the BGL is/was developed at Indiana University, in which case can I suggest you could lookup David Wild in the ChemoInformatics dept as he can comment on the utility of many graph algorithms mentioned above in the chemoinformatics domain. -----Original Message----- From: boost-users-bounces@lists.boost.org [mailto:boost-users-bounces@lists.boost.org] On Behalf Of Douglas Gregor Sent: 15 September 2005 03:02 To: boost-users@lists.boost.org Subject: Re: [Boost-users] Could the BGL graph algorithms be improved toautomatically work with VertexList = listS graphs? On Sep 14, 2005, at 7:26 PM, Jeremy Siek wrote:
Part of the problem is the language (C++), not the library. However, we may be able to fix this by going to extraordinary lengths. Though I can't say when one of the developers will have the time to do this. It's quite tedious trying to imagine all the ways an algorithm can be misused and try to trick the compiler into giving a good error message. This is one of the reasons I wrote a Ph.D. thesis about a new language.
And Jeremy neglected to mention that we're trying *very* hard to get some extensions into C++0x so that wretched error messages like these will be a thing of the past.
What do to BGL experts/implementers say? Would it not be **saner** to get these algorithms to work automatically no matter what graph type was chosen?
The problem with std::map is that it does not provide constant time access to the vertex index (it is logarithmic). Thus, the graph algorithm will run slower; it won't have the advertised time complexity. Then we'll get bug reports from people that are surprised by how slow the algorithm is.
It's definitely slower, but I think we need to give the usability issue more weight. I only recall ever having seen two cases where someone complained about the BGL being to slow: one was with betweenness_centrality, until we learned that the person had compiled without any optimizations; the other was with bundled properties slowing things down (due to the extra level of dispatch). On the other hand, we get questions every week about how to create property maps, especially edge property maps (because there's no way to avoid managing your own edge_index_t). We should get users hooked on the BGL first, then we can worry about getting maximal performance for them later. I've been thinking of a few ways to try to help users with creating and using property maps. It's possible that "all of them" is the right answer: 1) Make edge descriptors ordered (via <), so that users can make associative property maps more easily 2) Create templates vertex_property_map<T, Graph> and edge_property_map<T, Graph> that create external property maps without much effort from the user; in particular, that'll use an associative property map or an iterator property map depending on whether a vertex_index property is available. 3) As Tony mentions, make the algorithms a bit more lenient about the input graphs. They could use something like the class templates in #2, so long as we can still get maximal efficiency out of them when index maps are available. 4) Create new graph types (say, directed_graph<Vertex, Edge> and undirected_graph<Vertex, Edge>) that maintain vertex and edge index maps internally (as does the Python graph type). Doug _______________________________________________ Boost-users mailing list Boost-users@lists.boost.org http://lists.boost.org/mailman/listinfo.cgi/boost-users