Improve decision for which bound changes to immediately apply

Author: Opt-Mucca

highs/mip/HighsImplications.cpp

@@ -831,22 +831,33 @@ void HighsImplications::cleanupVub(HighsInt col, HighsInt vubCol,
 }
 
 void HighsImplications::applyImplications(HighsDomain& domain,
-                                          const HighsInt col, const bool val) {
+                                          const HighsInt col,
+                                          const HighsInt val) {
   assert(domain.isFixed(col));
 
-  auto checkImplication = [&](HighsDomainChange& domchg) -> bool {
+  auto checkImplication = [&](const HighsDomainChange& domchg) -> bool {
     assert(!domain.infeasible());
     if (domain.isFixed(domchg.column)) return false;
+    const bool isint =
+        domain.variableType(domchg.column) != HighsVarType::kContinuous;
+    // Directly change bounds on all integer columns. Only change continuous
+    // columns that fix the column, as changing their domains risks
+    // suppressing further bound changes found in propagation, e.g.,
+    // change [0, 100] -> [0, 50], propagation could tighten to [0, 48], but
+    // such a tightening would not be applied due to min boundRange improvement.
     if (domchg.boundtype == HighsBoundType::kLower) {
-      if (domchg.boundval >= domain.col_upper_[domchg.column]) {
-        // TODO: Long term: Should there be an implication reason?
-        HighsDomainChange domchgcpy = domchg;
-        domain.changeBound(domchgcpy, HighsDomain::Reason::unspecified());
+      if ((!isint && domchg.boundval >
+                         domain.col_upper_[domchg.column] - domain.feastol()) ||
+          (isint && domchg.boundval >
+                        domain.col_lower_[domchg.column] + domain.feastol())) {
+        domain.changeBound(domchg, HighsDomain::Reason::cliqueTable(col, val));
       }
     } else {
-      if (domchg.boundval <= domain.col_lower_[domchg.column]) {
-        HighsDomainChange domchgcpy = domchg;
-        domain.changeBound(domchgcpy, HighsDomain::Reason::unspecified());
+      if ((!isint && domchg.boundval <
+                         domain.col_lower_[domchg.column] + domain.feastol()) ||
+          (isint && domchg.boundval <
+                        domain.col_upper_[domchg.column] - domain.feastol())) {
+        domain.changeBound(domchg, HighsDomain::Reason::cliqueTable(col, val));
       }
     }
     return domain.infeasible();

highs/mip/HighsImplications.h

@@ -180,7 +180,7 @@ class HighsImplications {
                   HighsImplications::VarBound& vub, double ub, bool& redundant,
                   bool& infeasible, bool allowBoundChanges = true) const;
 
-  void applyImplications(HighsDomain& domain, HighsInt col, bool val);
+  void applyImplications(HighsDomain& domain, HighsInt col, HighsInt val);
 };
 
 #endif