Merge pull request #2530 from ERGO-Code/fix-2528

Fix 2528

Author: jajhall

check/TestIpm.cpp

@@ -200,3 +200,19 @@ TEST_CASE("test-2087", "[highs_ipm]") {
 
   h.resetGlobalScheduler(true);
 }
+
+TEST_CASE("test-2527", "[highs_ipm]") {
+  std::string filename =
+      std::string(HIGHS_DIR) + "/check/instances/primal1.mps";
+  Highs h;
+  //  h.setOptionValue("output_flag", dev_run);
+  REQUIRE(h.readModel(filename) == HighsStatus::kOk);
+  HighsLp lp = h.getLp();
+  lp.col_cost_.assign(lp.num_col_, 0);
+  REQUIRE(h.passModel(lp) == HighsStatus::kOk);
+  h.setOptionValue("solver", kIpmString);
+  h.setOptionValue("presolve", kHighsOffString);
+  REQUIRE(h.run() == HighsStatus::kOk);
+
+  h.resetGlobalScheduler(true);
+}

highs/ipm/ipx/basis.cc

@@ -119,12 +119,21 @@ Int Basis::Factorize() {
 
     // Build column pointers for passing to LU factorization.
     std::vector<Int> begin(m), end(m);
+    Int basis_num_nz = 0;
     for (Int i = 0; i < m; i++) {
         assert(basis_[i] >= 0);
         begin[i] = AI.begin(basis_[i]);
         end[i] = AI.end(basis_[i]);
+	basis_num_nz += (end[i]-begin[i]);
     }
 
+    std::stringstream h_logging_stream;
+    h_logging_stream.str(std::string());
+    h_logging_stream <<
+      " Start  factorization " << num_factorizations_+1 <<
+      ": nonzeros in basis = " << basis_num_nz << "\n";
+    control_.hIntervalLog(h_logging_stream);
+
     Int err = 0;                // return code
     while (true) {
         Int flag = lu_->Factorize(begin.data(), end.data(), AI.rowidx(),
@@ -151,6 +160,11 @@ Int Basis::Factorize() {
     }
     time_factorize_ += timer.Elapsed();
     factorization_is_fresh_ = true;
+    h_logging_stream.str(std::string());
+    h_logging_stream <<
+      " Finish factorization " << num_factorizations_ <<
+      ": fill factor = " << lu_->fill_factor() << "\n";
+    control_.hIntervalLog(h_logging_stream);
     return err;
 }
 

highs/ipm/ipx/lp_solver.cc

@@ -522,8 +522,8 @@ void LpSolver::BuildStartingBasis() {
         info_.status_ipm = IPX_STATUS_debug;
         return;
     }
-    basis_.reset(new Basis(control_, model_));
     control_.hLog(" Constructing starting basis...\n");
+    basis_.reset(new Basis(control_, model_));
     StartingBasis(iterate_.get(), basis_.get(), &info_);
     if (info_.errflag == IPX_ERROR_user_interrupt) {
         info_.errflag = 0;