Early plunge stop

cpp/src/branch_and_bound/branch_and_bound.cpp

@@ -1722,6 +1722,7 @@ void branch_and_bound_t<i_t, f_t>::plunge_with(bfs_worker_t<i_t, f_t>* worker,
     // relaxation
     // - The lower bound of the parent is lower or equal to its children
     worker->lower_bound = node_ptr->lower_bound;
+    fetch_max(exploration_stats_.max_node_depth, node_ptr->depth);
 
     if (node_ptr->lower_bound > upper_bound_.load()) {
       search_tree_.graphviz_node(settings_.log, node_ptr, "cutoff", node_ptr->lower_bound);
@@ -1772,6 +1773,18 @@ void branch_and_bound_t<i_t, f_t>::plunge_with(bfs_worker_t<i_t, f_t>* worker,
       break;
     }
 
+    i_t max_node_depth = exploration_stats_.max_node_depth;
+    i_t plunge_depth   = node_ptr->depth - start_node->depth;
+
+    if (plunge_depth >= settings_.bnb_min_plunge_depth * max_node_depth) {
+      f_t max_bound = lower_bound + settings_.bnb_plunge_gap_factor * (upper_bound - lower_bound);
+      if (node_ptr->lower_bound >= max_bound ||
+          plunge_depth >= settings_.bnb_max_plunge_depth * max_node_depth) {
+        stack.push_front(node_ptr);
+        break;
+      }
+    }
+
     decompress_vstatus(
       node_ptr->packed_vstatus, worker->leaf_problem.num_cols, worker->leaf_vstatus);
     assert(worker->leaf_vstatus.size() == worker->leaf_problem.num_cols);

cpp/src/branch_and_bound/worker.hpp

@@ -30,6 +30,7 @@ struct branch_and_bound_stats_t {
   omp_atomic_t<int64_t> nodes_unexplored = 0;
   // Tracks the number of nodes being solved by the workers at a given time
   omp_atomic_t<i_t> nodes_being_solved = 0;
+  omp_atomic_t<i_t> max_node_depth     = 0;
 
   omp_atomic_t<int64_t> total_simplex_iters = 0;
   omp_atomic_t<i_t> nodes_since_last_log    = 0;

cpp/src/dual_simplex/simplex_solver_settings.hpp

@@ -108,6 +108,9 @@ struct simplex_solver_settings_t {
       bnb_steal_chance(-1),
       bnb_nodes_per_steal(-1),
       bnb_max_steal_attempts(-1),
+      bnb_plunge_gap_factor(0.25),
+      bnb_min_plunge_depth(0.1),
+      bnb_max_plunge_depth(0.5),
       reliability_branching(-1),
       inside_mip(0),
       inside_submip(0),
@@ -222,6 +225,9 @@ struct simplex_solver_settings_t {
   f_t bnb_steal_chance;
   i_t bnb_nodes_per_steal;
   i_t bnb_max_steal_attempts;
+  f_t bnb_plunge_gap_factor;
+  f_t bnb_min_plunge_depth;
+  f_t bnb_max_plunge_depth;
 
   // Settings for the reliability branching.
   // - -1: automatic

cpp/src/utilities/omp_helpers.hpp

@@ -219,6 +219,7 @@ class omp_atomic_t {
 
   friend double fetch_min(omp_atomic_t<double>& atomic_var, double other);
   friend double fetch_max(omp_atomic_t<double>& atomic_var, double other);
+  friend double fetch_max(omp_atomic_t<int>& atomic_var, int other);
 };
 
 // Free non-template functions are necessary because of a clang 20 bug
@@ -246,6 +247,17 @@ inline double fetch_max(omp_atomic_t<double>& atomic_var, double other)
   return old;
 }
 
+inline double fetch_max(omp_atomic_t<int>& atomic_var, int other)
+{
+  double old;
+#pragma omp atomic compare capture
+  {
+    old = atomic_var.val;
+    if (other > atomic_var.val) { atomic_var.val = other; }
+  }
+  return old;
+}
+
 }  // namespace cuopt
 
 #endif