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Prevent parallel simplex when solving MIPs #3042

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Merged
jajhall merged 1 commit into from
May 27, 2026
Merged

Prevent parallel simplex when solving MIPs #3042

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16 changes: 0 additions & 16 deletions highs/lp_data/HighsOptions.h
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Original file line number Diff line number Diff line change
Expand Up @@ -438,9 +438,7 @@ struct HighsOptionsStruct {
HighsInt presolve_rule_off;
bool presolve_rule_logging;
bool presolve_remove_slacks;
bool simplex_initial_condition_check;
bool no_unnecessary_rebuild_refactor;
double simplex_initial_condition_tolerance;
double rebuild_refactor_solution_error_tolerance;
double dual_steepest_edge_weight_error_tolerance;
double dual_steepest_edge_weight_log_error_threshold;
Expand Down Expand Up @@ -605,9 +603,7 @@ struct HighsOptionsStruct {
presolve_rule_off(0),
presolve_rule_logging(false),
presolve_remove_slacks(false),
simplex_initial_condition_check(false),
no_unnecessary_rebuild_refactor(false),
simplex_initial_condition_tolerance(0.0),
rebuild_refactor_solution_error_tolerance(0.0),
dual_steepest_edge_weight_error_tolerance(0.0),
dual_steepest_edge_weight_log_error_threshold(0.0),
Expand Down Expand Up @@ -1523,24 +1519,12 @@ class HighsOptions : public HighsOptionsStruct {
kSimplexUnscaledSolutionStrategyMax);
records.push_back(record_int);

record_bool =
new OptionRecordBool("simplex_initial_condition_check",
"Perform initial basis condition check in simplex",
advanced, &simplex_initial_condition_check, true);
records.push_back(record_bool);

record_bool = new OptionRecordBool(
"no_unnecessary_rebuild_refactor",
"No unnecessary refactorization on simplex rebuild", advanced,
&no_unnecessary_rebuild_refactor, true);
records.push_back(record_bool);

record_double = new OptionRecordDouble(
"simplex_initial_condition_tolerance",
"Tolerance on initial basis condition in simplex", advanced,
&simplex_initial_condition_tolerance, 1.0, 1e14, kHighsInf);
records.push_back(record_double);

record_double = new OptionRecordDouble(
"rebuild_refactor_solution_error_tolerance",
"Tolerance on solution error when considering refactorization on "
Expand Down
3 changes: 0 additions & 3 deletions highs/mip/HighsMipSolverData.cpp
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Expand Up @@ -940,9 +940,6 @@ void HighsMipSolverData::runSetup() {
domain.clearChangedCols();

lp.getLpSolver().setOptionValue("presolve", kHighsOffString);
// lp.getLpSolver().setOptionValue("dual_simplex_cost_perturbation_multiplier",
// 0.0); lp.getLpSolver().setOptionValue("parallel", kHighsOnString);
lp.getLpSolver().setOptionValue("simplex_initial_condition_check", false);

checkObjIntegrality();
rootlpsol.clear();
Expand Down
19 changes: 12 additions & 7 deletions highs/simplex/HEkk.cpp
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Expand Up @@ -1723,13 +1723,18 @@ void HEkk::chooseSimplexStrategyThreads(const HighsOptions& options,
const HighsInt simplex_max_concurrency = options.simplex_max_concurrency;
HighsInt max_threads = highs::parallel::num_threads();

if (options.parallel == kHighsOnString &&
simplex_strategy == kSimplexStrategyDual) {
// The parallel strategy is on and the simplex strategy is dual so use
// PAMI if there are enough threads
if (max_threads >= kDualMultiMinConcurrency)
simplex_strategy = kSimplexStrategyDualMulti;
}
// Don't allow the parallel option to switch from
// kSimplexStrategyDual to kSimplexStrategyDualMulti so the MIP
// solver only ever uses serial simplex
//
// if (options.parallel == kHighsOnString &&
// simplex_strategy == kSimplexStrategyDual) {
// // The parallel strategy is on and the simplex strategy is dual so use
// // PAMI if there are enough threads
// if (max_threads >= kDualMultiMinConcurrency)
// simplex_strategy = kSimplexStrategyDualMulti;
// }

//
// If parallel strategies are used, the minimum concurrency will be
// set to be at least the minimum required for the strategy
Expand Down
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