From 82e08a102b913a1bf6d3b08d89826c7239218327 Mon Sep 17 00:00:00 2001 From: Francois Fleuret Date: Mon, 20 Aug 2012 20:49:15 -0700 Subject: [PATCH] Update. --- miniksp.cc | 104 +++++++++++++++++++++++++++++++++-------------------- 1 file changed, 65 insertions(+), 39 deletions(-) diff --git a/miniksp.cc b/miniksp.cc index f562423..4ec9423 100644 --- a/miniksp.cc +++ b/miniksp.cc @@ -20,7 +20,7 @@ // END_IP_HEADER // /////////////////////////////////////////////////////////////////////////// -#define VERBOSE +// #define VERBOSE #include #include @@ -42,6 +42,8 @@ typedef float scalar_t; #define ASSERT(x) #endif +// Adds to all the edge length the length of the shortest (which can +// be negative) void raise_es(int nb_edges, scalar_t *el) { scalar_t min_es = el[0]; for(int e = 1; e < nb_edges; e++) { @@ -52,30 +54,33 @@ void raise_es(int nb_edges, scalar_t *el) { } } +// Add to every edge length the differential of the psi function on it void add_dpsi_es(int nb_edges, scalar_t *el, int *ea, int *eb, scalar_t *psi) { for(int e = 0; e < nb_edges; e++) { el[e] += psi[ea[e]] - psi[eb[e]]; } } +// Find the shortest path in the graph and return in return_edge_back, +// for each vertex the edge to follow back from it to reach the source +// with the shortest path, and in return_dist the distance to the +// source. The edge lengths have to be positive. void find_shortest(int nb_vertices, int nb_edges, scalar_t *el, int *ea, int *eb, int source, int sink, - int *edge_back, scalar_t *dist) { + int *return_edge_back, scalar_t *return_dist) { for(int v = 0; v < nb_vertices; v++) { - // dist[v] = FLT_MAX; - dist[v] = 999; + dist[v] = FLT_MAX; + edge_back[v] = -1; } dist[source] = 0; - for(int v = 0; v < nb_vertices; v++) { - edge_back[v] = -1; - } - +#ifdef DEBUG for(int e = 0; e < nb_edges; e++) { - ASSERT(el[e] >= 0); + if(el[e] < 0) abort(); } +#endif int nb_changes; scalar_t d; @@ -98,43 +103,62 @@ void find_best_paths(int nb_vertices, int *edge_occupation) { scalar_t *dist = new scalar_t[nb_vertices]; int *edge_back = new int[nb_vertices]; - scalar_t *tmp_el = new scalar_t[nb_edges]; + scalar_t *positive_el = new scalar_t[nb_edges]; + scalar_t s; + int v; for(int e = 0; e < nb_edges; e++) { - tmp_el[e] = el[e]; + positive_el[e] = el[e]; edge_occupation[e] = 0; } - raise_es(nb_edges, tmp_el); + raise_es(nb_edges, positive_el); - scalar_t s; do { - find_shortest(nb_vertices, nb_edges, tmp_el, ea, eb, source, sink, edge_back, dist); - add_dpsi_es(nb_edges, tmp_el, ea, eb, dist); + find_shortest(nb_vertices, nb_edges, positive_el, ea, eb, source, sink, edge_back, dist); + add_dpsi_es(nb_edges, positive_el, ea, eb, dist); s = 0.0; + + // If the new path reaches the sink, we will backtrack on it to + // compute its score and invert edges + if(edge_back[sink] >= 0) { - int v = sink; + + v = sink; while(v != source) { int e = edge_back[v]; ASSERT(eb[e] == v); v = ea[e]; -#ifdef VERBOSE - cout << "INVERTING " << ea[e] << " -> " << eb[e] << " [" << el[e] << "]" << endl; -#endif s += el[e]; - int k = eb[e]; - eb[e] = ea[e]; - ea[e] = k; - tmp_el[e] = - tmp_el[e]; - edge_occupation[e] = 1 - edge_occupation[e]; } + + // We found a good path (score < 0), we revert the edges along + // the path and note that they are occupied + + if(s < 0) { + v = sink; +#ifdef VERBOSE + cout << "FOUND A PATH OF LENGTH " << s << endl; +#endif + while(v != source) { + int e = edge_back[v]; + ASSERT(eb[e] == v); + v = ea[e]; #ifdef VERBOSE - cout << "FOUND A PATH OF LENGTH " << s << endl; + cout << "INVERTING " << ea[e] << " -> " << eb[e] << " [" << el[e] << "]" << endl; #endif + int k = eb[e]; + eb[e] = ea[e]; + ea[e] = k; + positive_el[e] = - positive_el[e]; + el[e] = - el[e]; + edge_occupation[e] = 1 - edge_occupation[e]; + } + } } } while(s < 0); - delete[] tmp_el; + delete[] positive_el; delete[] dist; delete[] edge_back; } @@ -146,19 +170,20 @@ int main(int argc, char **argv) { exit(EXIT_FAILURE); } - ifstream file(argv[1]); + ifstream *file = new ifstream(argv[1]); int nb_edges, nb_vertices; int source, sink; - if(file.good()) { - file >> nb_vertices >> nb_edges; - file >> source >> sink; + if(file->good()) { + + (*file) >> nb_vertices >> nb_edges; + (*file) >> source >> sink; - cout << "nb_edges = " << nb_edges << endl; - cout << "nb_vertices = " << nb_vertices << endl; - cout << "source = " << source << endl; - cout << "sink = " << sink << endl; + cout << "INPUT nb_edges " << nb_edges << endl; + cout << "INPUT nb_vertices " << nb_vertices << endl; + cout << "INPUT source " << source << endl; + cout << "INPUT sink " << sink << endl; scalar_t *el = new scalar_t[nb_edges]; int *ea = new int[nb_edges]; @@ -166,10 +191,8 @@ int main(int argc, char **argv) { int *edge_occupation = new int[nb_edges]; for(int e = 0; e < nb_edges; e++) { - file >> ea[e] >> eb[e] >> el[e]; -#ifdef VERBOSE - cout << ea[e] << " -> " << eb[e] << " [" << el[e] << "]" << endl; -#endif + (*file) >> ea[e] >> eb[e] >> el[e]; + cout << "INPUT_EDGE " << ea[e] << " " << eb[e] << " " << el[e] << endl; } find_best_paths(nb_vertices, nb_edges, el, ea, eb, source, sink, @@ -177,7 +200,7 @@ int main(int argc, char **argv) { for(int e = 0; e < nb_edges; e++) { if(edge_occupation[e]) { - cout << ea[e] << " " << eb[e] << endl; + cout << "RESULT_OCCUPIED_EDGE " << ea[e] << " " << eb[e] << endl; } } @@ -189,9 +212,12 @@ int main(int argc, char **argv) { } else { cerr << "Can not open " << argv[1] << endl; + + delete file; exit(EXIT_FAILURE); } + delete file; exit(EXIT_SUCCESS); } -- 2.20.1