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Fix explored nodes counter #570

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Merged
merged 7 commits into from
Nov 26, 2025
Merged

Fix explored nodes counter #570

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6b51863
fixed the node exploration count, so it is only update after solving …
nguidotti Nov 6, 2025
d110e4a
add missing initialization
nguidotti Nov 6, 2025
bd697c9
Merge branch 'main' into fix-explored-counter
nguidotti Nov 6, 2025
9734677
added missing counter
nguidotti Nov 6, 2025
c25d295
Merge remote-tracking branch 'cuopt/release/25.12' into fix-explored-…
nguidotti Nov 25, 2025
66fe769
merge 2
nguidotti Nov 25, 2025
d499bea
updated counter based on reviewers feedback
nguidotti Nov 25, 2025
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45 changes: 30 additions & 15 deletions cpp/src/dual_simplex/branch_and_bound.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -697,17 +697,17 @@ void branch_and_bound_t<i_t, f_t>::exploration_ramp_up(search_tree_t<i_t, f_t>*
// to repair the heuristic solution.
repair_heuristic_solutions();

f_t lower_bound = node->lower_bound;
f_t upper_bound = get_upper_bound();
f_t rel_gap = user_relative_gap(original_lp_, upper_bound, lower_bound);
f_t abs_gap = upper_bound - lower_bound;
i_t nodes_explored = (++stats_.nodes_explored);
i_t nodes_unexplored = (--stats_.nodes_unexplored);
stats_.nodes_since_last_log++;
f_t lower_bound = node->lower_bound;
f_t upper_bound = get_upper_bound();
f_t rel_gap = user_relative_gap(original_lp_, upper_bound, lower_bound);
f_t abs_gap = upper_bound - lower_bound;

if (lower_bound > upper_bound || rel_gap < settings_.relative_mip_gap_tol) {
search_tree->graphviz_node(settings_.log, node, "cutoff", node->lower_bound);
search_tree->update_tree(node, node_status_t::FATHOMED);
++stats_.nodes_explored;
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@chris-maes chris-maes Nov 8, 2025

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This is a bit strange. I think of nodes explored as the number of nodes we have solved, or perhaps proved infeasible through node presolve. If we are fathoming the node here I would not count it as explored.

--stats_.nodes_unexplored;
++stats_.nodes_since_last_log;
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@chris-maes chris-maes Nov 8, 2025

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Same here. The purpose of nodes since last log is for us to print every so often in a deterministic way. Here we did no work, so I don't think we want to increase this counter.

return;
}

Expand All @@ -717,15 +717,14 @@ void branch_and_bound_t<i_t, f_t>::exploration_ramp_up(search_tree_t<i_t, f_t>*
if (((stats_.nodes_since_last_log >= 10 || abs_gap < 10 * settings_.absolute_mip_gap_tol) &&
(time_since_last_log >= 1)) ||
(time_since_last_log > 30) || now > settings_.time_limit) {
// Check if no new node was explored until now. If this is the case,
// only the last thread should report the progress
if (stats_.nodes_explored.load() == nodes_explored) {
stats_.nodes_since_last_log = 0;
stats_.last_log = tic();
bool should_report = should_report_.exchange(false);
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@chris-maes chris-maes Nov 8, 2025

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Do we need to have member variable to decide if we should log? I think this is increasing the complexity of the code for little return.

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@nguidotti nguidotti Nov 25, 2025

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Since this piece of code is running by multiple threads, the atomic here prevent multiple reports from happening (potentially out-of-order). But I agree that it is an imperfect solution. I will probably change when the ramp-up phase is reworked or the report is moved to a separated thread.


if (should_report) {
f_t obj = compute_user_objective(original_lp_, upper_bound);
f_t user_lower = compute_user_objective(original_lp_, root_objective_);
std::string gap_user = user_mip_gap<f_t>(obj, user_lower);
i_t nodes_explored = stats_.nodes_explored;
i_t nodes_unexplored = stats_.nodes_unexplored;

settings_.log.printf(" %10d %10lu %+13.6e %+10.6e %6d %7.1e %s %9.2f\n",
nodes_explored,
Expand All @@ -736,6 +735,10 @@ void branch_and_bound_t<i_t, f_t>::exploration_ramp_up(search_tree_t<i_t, f_t>*
nodes_explored > 0 ? stats_.total_lp_iters / nodes_explored : 0,
gap_user.c_str(),
now);

stats_.nodes_since_last_log = 0;
stats_.last_log = tic();
should_report_ = true;
}
}

Expand Down Expand Up @@ -775,6 +778,10 @@ void branch_and_bound_t<i_t, f_t>::exploration_ramp_up(search_tree_t<i_t, f_t>*
mutex_heap_.unlock();
}
}

++stats_.nodes_explored;
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@chris-maes chris-maes Nov 8, 2025

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Nit: is there a reason why all of these are ++x instead x++?

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@chris-maes chris-maes Nov 8, 2025

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Why are we incrementing the nodes explored here at all?

--stats_.nodes_unexplored;
++stats_.nodes_since_last_log;
}

template <typename i_t, typename f_t>
Expand Down Expand Up @@ -806,13 +813,13 @@ void branch_and_bound_t<i_t, f_t>::explore_subtree(i_t task_id,
// - The lower bound of the parent is lower or equal to its children
assert(task_id < local_lower_bounds_.size());
local_lower_bounds_[task_id] = lower_bound;
i_t nodes_explored = (++stats_.nodes_explored);
i_t nodes_unexplored = (--stats_.nodes_unexplored);
stats_.nodes_since_last_log++;

if (lower_bound > upper_bound || rel_gap < settings_.relative_mip_gap_tol) {
search_tree.graphviz_node(settings_.log, node_ptr, "cutoff", node_ptr->lower_bound);
search_tree.update_tree(node_ptr, node_status_t::FATHOMED);
++stats_.nodes_explored;
--stats_.nodes_unexplored;
++stats_.nodes_since_last_log;
continue;
}

Expand All @@ -827,6 +834,9 @@ void branch_and_bound_t<i_t, f_t>::explore_subtree(i_t task_id,
f_t obj = compute_user_objective(original_lp_, upper_bound);
f_t user_lower = compute_user_objective(original_lp_, get_lower_bound());
std::string gap_user = user_mip_gap<f_t>(obj, user_lower);
i_t nodes_explored = stats_.nodes_explored;
i_t nodes_unexplored = stats_.nodes_unexplored;

settings_.log.printf(" %10d %10lu %+13.6e %+10.6e %6d %7.1e %s %9.2f\n",
nodes_explored,
nodes_unexplored,
Expand Down Expand Up @@ -889,6 +899,10 @@ void branch_and_bound_t<i_t, f_t>::explore_subtree(i_t task_id,
stack.push_front(second);
stack.push_front(first);
}

++stats_.nodes_explored;
--stats_.nodes_unexplored;
++stats_.nodes_since_last_log;
}
}

Expand Down Expand Up @@ -1174,6 +1188,7 @@ mip_status_t branch_and_bound_t<i_t, f_t>::solve(mip_solution_t<i_t, f_t>& solut
min_diving_queue_size_ = 4 * settings_.num_diving_threads;
status_ = mip_exploration_status_t::RUNNING;
lower_bound_ceiling_ = inf;
should_report_ = true;

#pragma omp parallel num_threads(settings_.num_threads)
{
Expand Down
2 changes: 2 additions & 0 deletions cpp/src/dual_simplex/branch_and_bound.hpp
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Expand Up @@ -209,6 +209,8 @@ class branch_and_bound_t {
// Global status of the solver.
omp_atomic_t<mip_exploration_status_t> status_;

omp_atomic_t<bool> should_report_;

// In case, a best-first thread encounters a numerical issue when solving a node,
// its blocks the progression of the lower bound.
omp_atomic_t<f_t> lower_bound_ceiling_;
Expand Down