Recovered IIS use of optionChangeAction

Author: jajhall

check/TestUserScale.cpp

@@ -4,7 +4,7 @@
 #include "Highs.h"
 #include "catch.hpp"
 
-const bool dev_run = true;  // false;
+const bool dev_run = false;
 const double inf = kHighsInf;
 
 bool doubleEqual0(const double v0, const double v1) {

highs/Highs.h

@@ -1705,8 +1705,7 @@ class Highs {
 
   HighsStatus handleInfCost();
   void restoreInfCost(HighsStatus& return_status);
-  // Retain trivial optionChangeAction() in case it's useful later
-  HighsStatus optionChangeAction() const { return HighsStatus::kOk; };
+  HighsStatus optionChangeAction();
 
   HighsStatus userScaleModel(HighsUserScaleData& data);
   HighsStatus userScaleSolution(HighsUserScaleData& data,

highs/lp_data/HighsInterface.cpp

@@ -2944,6 +2944,12 @@ HighsStatus Highs::handleInfCost() {
   return HighsStatus::kOk;
 }
 
+HighsStatus Highs::optionChangeAction() {
+  if (this->iis_.valid_ && options_.iis_strategy != this->iis_.strategy_)
+    this->iis_.invalidate();
+  return HighsStatus::kOk;
+}
+
 void Highs::restoreInfCost(HighsStatus& return_status) {
   HighsLp& lp = this->model_.lp_;
   HighsBasis& basis = this->basis_;