Merge pull request #40 from jabo17/fixing_wmis_bnr_errors

fix two bugs in weighted branch and reduce

Author: ernestine-grossmann

wmis/app/branch_reduce.cpp

@@ -93,7 +93,7 @@ int main(int argn, char **argv) {
 
         branch_and_reduce_algorithm reducer(G, mis_config);
         reducer.run_branch_reduce();
-        NodeWeight MWIS_weight = reducer.get_current_is_weight();
+        NodeWeight MWIS_weight = reducer.get_is_weight();
 
         auto end = std::chrono::system_clock::now();
 

wmis/app/weighted_ls.cpp

@@ -81,7 +81,7 @@ NodeWeight perform_reduction(std::unique_ptr<branch_and_reduce_algorithm>& reduc
 		exit(1);
 	}
 
-	NodeWeight is_weight = reducer->get_current_is_weight();
+	NodeWeight is_weight = reducer->get_is_weight();
 
 	return is_weight;
 }

wmis/lib/mis/kernel/branch_and_reduce_algorithm.cpp

@@ -728,19 +728,19 @@ void branch_and_reduce_algorithm::restore_best_local_solution() {
 
 void branch_and_reduce_algorithm::restore_best_global_solution() {
 	status = std::move(global_status);
-	status.modified_queue.pop_back();
+    status.modified_queue.pop_back();
 
 	while (!status.modified_queue.empty()) {
 		NodeID node = status.modified_queue.back();
-		status.modified_queue.pop_back();
+        status.modified_queue.pop_back();
 
 		if (status.node_status[node] == IS_status::folded) {
 			auto type = status.folded_queue.back();
-			status.folded_queue.pop_back();
-			status.reductions[global_reduction_map[type]]->apply(this);
+            status.folded_queue.pop_back();
+            status.reductions[global_reduction_map[type]]->apply(this);
 		}
 		else {
-			status.graph.restore_node(node);
+            status.graph.restore_node(node);
 		}
 	}
 }
@@ -749,6 +749,11 @@ NodeWeight branch_and_reduce_algorithm::get_current_is_weight() const {
 	return global_status.is_weight + global_status.reduction_offset;
 }
 
+NodeWeight branch_and_reduce_algorithm::get_is_weight() const {
+    // after restoring global best solution, global status was moved to status
+    return status.is_weight + status.reduction_offset;
+}
+
 void branch_and_reduce_algorithm::build_global_graph_access() {
 	global_mapping.resize(global_status.remaining_nodes, 0);
 	std::swap(status, global_status);

wmis/lib/mis/kernel/branch_and_reduce_algorithm.h

@@ -194,6 +194,8 @@ class branch_and_reduce_algorithm {
 	void disable_cout();
 	void enable_cout();
 
+    NodeWeight get_current_is_weight() const;
+
 public:
 	branch_and_reduce_algorithm(graph_access& G, const MISConfig& config, bool called_from_fold = false);
 
@@ -203,7 +205,7 @@ class branch_and_reduce_algorithm {
 	static size_t run_ils(const MISConfig& config, graph_access& G, sized_vector<NodeID>& tmp_buffer, size_t max_swaps);
 	static void greedy_initial_is(graph_access& G, sized_vector<NodeID>& tmp_buffer);
 
-	NodeWeight get_current_is_weight() const;
+	NodeWeight get_is_weight() const;
 	void reverse_reduction(graph_access & G, graph_access & reduced_G, std::vector<NodeID> & reverse_mapping);
 	void apply_branch_reduce_solution(graph_access & G);
 

wmis/lib/mis/kernel/reductions.cpp

@@ -396,24 +396,36 @@ void fold2_reduction::restore(branch_and_reduce_algorithm* br_alg) {
 }
 
 void fold2_reduction::apply(branch_and_reduce_algorithm* br_alg) {
-	auto& status = br_alg->status;
-	auto nodes = restore_vec.back().nodes;
-	auto main_status = status.node_status[nodes.main];
-	restore(br_alg);
-
-	if (main_status == IS_status::included) {
-		status.node_status[nodes.main] = IS_status::excluded;
-		status.node_status[nodes.rest[0]] = IS_status::included;
-		status.node_status[nodes.rest[1]] = IS_status::included;
-
-		status.is_weight += status.weights[nodes.rest[0]] + status.weights[nodes.rest[1]];
-	} else {
-		status.node_status[nodes.main] = IS_status::included;
-		status.node_status[nodes.rest[0]] = IS_status::excluded;
-		status.node_status[nodes.rest[1]] = IS_status::excluded;
-
-		status.is_weight += status.weights[nodes.main];
-	}
+#ifndef NDEBUG
+    NodeWeight previous_is_weight = br_alg->status.is_weight + br_alg->status.reduction_offset;
+#endif
+
+    auto& status = br_alg->status;
+    auto nodes = restore_vec.back().nodes;
+    auto main_status = status.node_status[nodes.main];
+    restore(br_alg);
+
+    if (main_status == IS_status::included) {
+        status.node_status[nodes.main] = IS_status::excluded;
+        status.node_status[nodes.rest[0]] = IS_status::included;
+        status.node_status[nodes.rest[1]] = IS_status::included;
+
+        // weight of folded vertex was added to is_weight while reducing:
+        //  status.is_weight += status.weights[nodes.rest[0]] + status.weights[nodes.rest[1]] - status.weights[nodes.main]
+        // only need to add status.weights[nodes.main] to is_weight
+        status.is_weight += status.weights[nodes.main];
+        // old: status.is_weight += status.weights[nodes.rest[0]] + status.weights[nodes.rest[1]];
+    } else {
+        status.node_status[nodes.main] = IS_status::included;
+        status.node_status[nodes.rest[0]] = IS_status::excluded;
+        status.node_status[nodes.rest[1]] = IS_status::excluded;
+
+        status.is_weight += status.weights[nodes.main];
+    }
+#ifndef NDEBUG
+    // invariant that has to hold
+    ASSERT_TRUE(br_alg->status.is_weight + br_alg->status.reduction_offset == previous_is_weight);
+#endif
 }
 
 bool clique_reduction::reduce(branch_and_reduce_algorithm* br_alg) {
@@ -780,7 +792,7 @@ bool generalized_neighborhood_reduction::reduce(branch_and_reduce_algorithm* br_
 				continue;
 			}
 
-			if (status.weights[v] >= neighborhood_br_alg.get_current_is_weight())
+			if (status.weights[v] >= neighborhood_br_alg.get_is_weight())
 				br_alg->set(v, IS_status::included);
 		}
 	}
@@ -845,7 +857,7 @@ bool generalized_fold_reduction::reduce(branch_and_reduce_algorithm* br_alg) {
 				continue;
 			}
 
-			NodeWeight MWIS_weight = neighborhood_br_alg.get_current_is_weight();
+			NodeWeight MWIS_weight = neighborhood_br_alg.get_is_weight();
 			NodeWeight min_MWIS_neighbor_weight = std::numeric_limits<NodeWeight>::max();
 
 			if (status.weights[v] >= MWIS_weight) {
@@ -889,7 +901,7 @@ bool generalized_fold_reduction::reduce(branch_and_reduce_algorithm* br_alg) {
 					std::cerr << "%generalized_fold_reduction br_call loop time out" << std::endl;
 					check_failed = true;
 				}
-				else if (neighborhood_br_alg.get_current_is_weight() >= status.weights[v]) {
+				else if (neighborhood_br_alg.get_is_weight() >= status.weights[v]) {
 					check_failed = true;
 				}
 
@@ -942,7 +954,7 @@ bool generalized_fold_reduction::reduce(branch_and_reduce_algorithm* br_alg) {
 					}
 					else {
 						// if the weight of every MWIS in N(v) which contains "node" is smaller than w(v) then we can remove "node"
-						remove_node = neighborhood_br_alg.get_current_is_weight() + status.weights[node] <= status.weights[v];
+						remove_node = neighborhood_br_alg.get_is_weight() + status.weights[node] <= status.weights[v];
 					}
 
 					for (const NodeID neighbor : status.graph[node]) {
@@ -1058,6 +1070,9 @@ void generalized_fold_reduction::restore(branch_and_reduce_algorithm* br_alg) {
 }
 
 void generalized_fold_reduction::apply(branch_and_reduce_algorithm* br_alg) {
+#ifndef NDEBUG
+    NodeWeight previous_is_weight = br_alg->status.is_weight + br_alg->status.reduction_offset;
+#endif
 	auto& status = br_alg->status;
 	auto nodes = restore_vec.back().nodes;
 	auto MWIS_weight = restore_vec.back().MWIS_weight;
@@ -1071,7 +1086,8 @@ void generalized_fold_reduction::apply(branch_and_reduce_algorithm* br_alg) {
 			status.node_status[node] = IS_status::included;
 		}
 
-		status.is_weight += MWIS_weight;
+        status.is_weight += status.weights[nodes.main]; // for details see fold2::apply
+		// wrong: status.is_weight += MWIS_weight;
 	} else {
 		status.node_status[nodes.main] = IS_status::included;
 
@@ -1081,4 +1097,8 @@ void generalized_fold_reduction::apply(branch_and_reduce_algorithm* br_alg) {
 
 		status.is_weight += status.weights[nodes.main];
 	}
+#ifndef NDEBUG
+    // invariant that has to hold
+    ASSERT_TRUE(br_alg->status.is_weight + br_alg->status.reduction_offset == previous_is_weight);
+#endif
 }