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March 2009

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262 discussions

[graph] kolmogorov_max_flow color map, gray state
by Sebastian Nowozin 01 Mar '09

01 Mar '09

Hello everybody, I use the boost graph library to find the linear min-cut of a directed graph with exactly one source and one sink node (s-t min-cut). For this, I setup a linear max-flow problem and solve it using kolmogorov_max_flow. The color_map property is supposed to be usable to recover the edge cut set from the max-flow solution, see the description on http://www.boost.org/doc/libs/1_38_0/libs/graph/doc/kolmogorov_max_flow.html However, as long as there are no vertices colored "gray" I can simply tell which side of the cut a node belongs to by doing something like: std::vector<default_color_type> color(num_vertices(g_ab)); double flow = kolmogorov_max_flow(g_ab, alpha_vertex, beta_vertex, color_map(&color[0])); bool is_left = (color[node_desc] == tc_color_traits::white()); bool is_right = (color[node_desc] == tc_color_traits::black()); And this works just fine. For some problems I am solving there are gray nodes, and I do not know how to determine their position relative to the edge cut set. Is there a code example available in the boost repository or has anyone had this problem? It seems surprising to me that obtaining the edge cut set of a linear min-cut problem seems to be non-trivial using the boost graph library. I must be doing something wrong. Thanks, Sebastian

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Spirit, semantic actions and C++ classes
by Claudio La Rosa 01 Mar '09

01 Mar '09

I am writing a class that implements a simple parser. In the costructor I created the rule and the parser...and I recall the functions for the semantic actions. I have implemented this function as member funcions and, for recalled it, I use a pointer to my member function in this manner: #include <boost/spirit.hpp> using namespace boost::spirit; class MYParser { private: //main rules rule<const char*> rLine, rComment; //This are the “semantic action” void AnnounceComment(char const*, char const*); // ...and this is the pointer to my “semantic action” void (SQLParser::*ptrAnnounceComment)(char const*, char const*); public: MYParser(void); //distuttore ͠ MYParser(); }; MYParser::MYParser() { //(SQLParser::*ptrAnnounceComment)();// = &SQLParser::AnnounceComment; //AnnounceComment is my Member functions ptrAnnounceComment=&SQLParser::AnnounceComment; //make the parser rLine = rComment; rSpazi = *space_p; rTerminal = !ch_p(';'); //commento SQL fino a fine riga rComment = str_p("#") >> (*anychar_p)[ this->*ptrAnnounceComment ]; //... } I obtain an error: “no match for ‘operator[]’ in ‘boost::spirit::operator* [with S = boost::spirit::anychar_parser](((const boost::spirit::parser<boost::spirit::anychar_parser>&)((const boost::spirit::parser<boost::spirit::anychar_parser>*)(& boost::spirit::anychar_p))))[((SQLParser*)this)->*((SQLParser*)this)->SQLParser::ptrAnnounceComment]’” on the line: rComment = str_p("#") >> (*anychar_p)[ this->*ptrAnnounceComment ]; But..why? I have only a little experience with C++ and spirit :-( Ciao Claudio -- View this message in context: http://www.nabble.com/Spirit%2C-semantic-actions-and-C%2B%2B-classes-tp2226… Sent from the Boost - Dev mailing list archive at Nabble.com.

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