[Boost-users] [BGL] predecessor map from a view on a multi_array

Subject: [Boost-users] [BGL] predecessor map from a view on a multi_array
From: Geoff Hilton (geoff.hilton_at_[hidden])
Date: 2010-02-01 20:48:01

Hi, I'm currently using MSVC9 and the code listed below doesn't compile, 
instead producing the following errors and warnings:

Warning	1	warning C4100: 'x' : unreferenced formal parameter 
c:\program files\boost\boost_1_41_0\boost\concept\detail\msvc.hpp	20	test
Warning	2	warning C4100: 'id' : unreferenced formal parameter 
c:\program 
files\boost\boost_1_41_0\boost\graph\dag_shortest_paths.hpp	86	test
Error	3	error C2440: '<function-style-cast>' : cannot convert from 
'int' to 'D'	c:\program files\microsoft visual studio 
9.0\vc\include\limits	109	test

I know MSVC has issues with named parameters among other things, but I 
haven't been able to get it to compile with the non-named-parameters 
overload either, in this instance.
What am I misusing and how am I misusing it? Also, I get the impression 
that the default combiner/comparer may be unsafe for floating-point 
comparisons and addition (with respect to over/underflow and comparing 
floating point values, I seem to recall it being a good idea never to 
compare with direct equalities, eg. x == infinity because of rounding 
issues). Might it be a good idea to further specialize appropriate areas 
of the algorithm code to account for this, or am I 
over-generalizing(specializing?)? How about a specialized closed_plus<> 
in relax.hpp which makes the comparisons more safely for floats and 
doubles (since both parameters "a" and "b" of closed_plus must be of 
type T anyway)?

#include <boost/graph/adjacency_list.hpp>
#include <boost/graph/dag_shortest_paths.hpp>
#include <boost/multi_array.hpp>

namespace geoff {
typedef boost::adjacency_list<boost::vecS, boost::vecS, boost::directedS
                              ,boost::no_property, float> Graph;
typedef 
boost::multi_array<boost::graph_traits<Graph>::vertex_descriptor, 2U> 
PredecessorsMatrix;

typedef PredecessorsMatrix::array_view<1>::type PredecessorMap;
} //namespace geoff

int main(int /*argc*/, char* /*argv*/[])
{
   const std::size_t num_agents = 3;
   geoff::Graph graph;
   geoff::PredecessorsMatrix 
per_agent_matrix(boost::extents[num_agents][boost::num_vertices(graph)]);
   geoff::PredecessorsMatrix::index_gen indices;
   std::size_t agent_index = 0U;
   geoff::PredecessorMap agent_x_predecessors = 
per_agent_matrix[indices[agent_index][boost::multi_array_types::index_range()]];
   boost::dag_shortest_paths(graph, 0, 
boost::predecessor_map(agent_x_predecessors));
}
Thanks very much,
Geoff