fix: valid syntax in the export to graphviz

src/main.cpp

@@ -234,6 +234,7 @@ void ComputeAbstractPaths(const string& net_file, int bound,
   auto paths_time = GetTime() - start_paths_time;
   cout << " done\nTime for computing observable paths: " << paths_time
        << " seconds\n";
+  sog.ExportGraphToDotFile("./sog.dot");
 
   // add abstract paths
   cout << "\nComputing abstract paths ...";

src/sog.cpp

@@ -90,7 +90,7 @@ void SOG::PrintGraph(Aggregate *state, size_t counter) {
 
 void SOG::ExportGraphToDotFile(const std::string &filename) const {
   // Open file for writing
-  std::ofstream file(filename + ".dot");
+  std::ofstream file(filename);
 
   // Check if the file opened successfully
   if (!file.is_open()) {
@@ -101,16 +101,19 @@ void SOG::ExportGraphToDotFile(const std::string &filename) const {
   std::cout << "the graph contains: " << nb_states << " states\n";
   file << "digraph reachab_graph {" << '\n';
 
+  // Add the initial node (start point)
+  file << "  start [shape=point, width=0];\n\n";
+  file << "  start -> ag_" << initial_state->state.id() << ";\n";
+
   for (const auto *aggr : states) {
     for (const auto &edge : aggr->successors) {
-      file << "ag_" << aggr->state.id() << " -> "
-           << "ag_" << edge.state->state.id() << " [ label =  \"t"
-           << edge.transition + 1 << "\"]" << '\n';
+      file << "  ag_" << aggr->state.id() << " -> "
+           << "ag_" << edge.state->state.id() << " [ label = \"t"
+           << edge.transition + 1 << "\"];" << '\n';
     }
   }
 
-  file << "ag_" << initial_state->state.id() << "[initialstate]\n";
-  file << " }\n";
+  file << "}\n";
   file.close();
 }