Merge pull request #2525 from ERGO-Code/fix-force-highs-solution-basis-size

Fix `Highs::forceHighsSolutionBasisSize`

Author: jajhall

check/TestBasis.cpp

@@ -315,3 +315,43 @@ void testBasisRestart(Highs& highs, const std::string& basis_file,
 
   REQUIRE(info.simplex_iteration_count == 0);
 }
+
+TEST_CASE("Basis-read", "[highs_basis_data]") {
+  // Duplicates test_read_basis in test_highspy.py
+  const std::string test_name = Catch::getResultCapture().getCurrentTestName();
+
+  HighsLp lp;
+  lp.num_col_ = 2;
+  lp.num_row_ = 2;
+  lp.col_cost_ = {0, 1};
+  lp.col_lower_.assign(lp.num_col_, -kHighsInf);
+  lp.col_upper_.assign(lp.num_col_, kHighsInf);
+  lp.row_lower_ = {2, 0};
+  lp.row_upper_.assign(lp.num_row_, kHighsInf);
+  lp.a_matrix_.start_ = {0, 2, 4};
+  lp.a_matrix_.index_ = {0, 1, 0, 1};
+  lp.a_matrix_.value_ = {-1, 1, 1, 1};
+
+  HighsBasisStatus status_before = HighsBasisStatus::kNonbasic;
+  HighsBasisStatus status_after = HighsBasisStatus::kBasic;
+  Highs h1;
+  const HighsBasis& basis1 = h1.getBasis();
+  h1.passModel(lp);
+  REQUIRE(basis1.col_status[0] == status_before);
+  h1.run();
+  REQUIRE(basis1.col_status[0] == status_after);
+
+  Highs h2;
+  const HighsBasis& basis2 = h2.getBasis();
+  h2.passModel(lp);
+  REQUIRE(basis2.col_status[0] == status_before);
+
+  const std::string basis_file = test_name + ".bas";
+  h1.writeBasis(basis_file);
+  h2.readBasis(basis_file);
+  REQUIRE(basis2.col_status[0] == status_after);
+
+  std::remove(basis_file.c_str());
+  h1.resetGlobalScheduler(true);
+  h2.resetGlobalScheduler(true);
+}

highs/lp_data/Highs.cpp

@@ -4368,23 +4368,39 @@ void Highs::newHighsBasis() {
 // model, and that the HiGHS basis is kept up-to-date with any solved
 // basis
 void Highs::forceHighsSolutionBasisSize() {
-  // Ensure that the HiGHS solution vectors are the right size
-  solution_.col_value.resize(model_.lp_.num_col_);
-  solution_.row_value.resize(model_.lp_.num_row_);
-  solution_.col_dual.resize(model_.lp_.num_col_);
-  solution_.row_dual.resize(model_.lp_.num_row_);
-  // Ensure that the HiGHS basis vectors are the right size,
-  // invalidating the basis if they aren't
-  if (basis_.col_status.size() != static_cast<size_t>(model_.lp_.num_col_)) {
-    basis_.col_status.resize(model_.lp_.num_col_);
-    basis_.valid = false;
-    basis_.useful = false;
+  // Ensure that the HiGHS solution and basis vectors are the right size
+  //
+  // If the column or row, values or duals, are increased in size,
+  // ensure that values are assigned to the new entries, and that
+  // validity and status values are over-written in HighsSolution,
+  // HighsBasis and HighsInfo
+  const HighsInt num_col = this->model_.lp_.num_col_;
+  const HighsInt num_row = this->model_.lp_.num_row_;
+  // Values
+  if (solution_.col_value.size() < static_cast<size_t>(num_col) ||
+      solution_.row_value.size() < static_cast<size_t>(num_row)) {
+    solution_.value_valid = false;
+    info_.primal_solution_status = kSolutionStatusNone;
+  }
+  solution_.col_value.resize(num_col, 0);
+  solution_.row_value.resize(num_row, 0);
+  // Duals
+  if (solution_.col_dual.size() < static_cast<size_t>(num_col) ||
+      solution_.row_dual.size() < static_cast<size_t>(num_row)) {
+    solution_.dual_valid = false;
+    info_.dual_solution_status = kSolutionStatusNone;
   }
-  if (basis_.row_status.size() != static_cast<size_t>(model_.lp_.num_row_)) {
-    basis_.row_status.resize(model_.lp_.num_row_);
+  solution_.col_dual.resize(num_col, 0);
+  solution_.row_dual.resize(num_row, 0);
+  // Basis
+  if (basis_.col_status.size() != static_cast<size_t>(num_col) ||
+      basis_.row_status.size() != static_cast<size_t>(num_row)) {
     basis_.valid = false;
     basis_.useful = false;
+    info_.basis_validity = kBasisValidityInvalid;
   }
+  basis_.col_status.resize(num_col, HighsBasisStatus::kNonbasic);
+  basis_.row_status.resize(num_row, HighsBasisStatus::kBasic);
 }
 
 void Highs::setHighsModelStatusAndClearSolutionAndBasis(

tests/test_highspy.py

@@ -1004,7 +1004,7 @@ def test_write_basis_after_running(self):
     def test_read_basis(self):
         if platform == "linux" or platform == "darwin":
             # Read basis from one run model into an unrun model
-            expected_status_before = highspy.HighsBasisStatus.kLower
+            expected_status_before = highspy.HighsBasisStatus.kNonbasic
             expected_status_after = highspy.HighsBasisStatus.kBasic
 
             h1 = self.get_basic_model()