Methods receiving matrix data where only small values are explicit ze…

…ros (so removed internally) are now silent and return HighsStatus::kOk (since internal matrix is exact)

FEATURES.md

@@ -16,6 +16,13 @@ Added `Highs::feasibilityRelaxation` to solve the problem of minimizing a (possi
 
 Added Python utility `examples/plot_highs_log.py` (due to @Thell) to visualise progress of the MIP solver.
 
+Added minimal documentation of solvers and how simplex variants can be run
+
+Methods receiving matrix data where only small values are explicit zeros (so removed internally) are now silent and return HighsStatus::kOk (since internal matrix is exact)
+
+
+
+
 
 
 

check/TestLpModification.cpp

@@ -1937,3 +1937,20 @@ TEST_CASE("modify-empty-model", "[highs_data]") {
   REQUIRE(highs.changeColBounds(0, 1, 1) == HighsStatus::kError);
   REQUIRE(highs.changeRowBounds(0, 1, 1) == HighsStatus::kError);
 }
+
+TEST_CASE("zero-matrix-entries", "[highs_data]") {
+  Highs highs;
+  highs.setOptionValue("output_flag", dev_run);
+  HighsLp lp;
+  lp.num_col_ = 2;
+  lp.num_row_ = 2;
+  lp.col_cost_ = {0, 0};
+  lp.col_lower_ = {0, 0};
+  lp.col_upper_ = {1, 1};
+  lp.row_lower_ = {-kHighsInf, -kHighsInf};
+  lp.row_upper_ = {5, 8};
+  lp.a_matrix_.start_ = {0, 2, 4};
+  lp.a_matrix_.index_ = {0, 1, 0, 1};
+  lp.a_matrix_.value_ = {1, 0, 0, 1};
+  REQUIRE(highs.passModel(lp) == HighsStatus::kOk);
+}

check/TestLpValidation.cpp

@@ -94,7 +94,7 @@ TEST_CASE("LP-dimension-validation", "[highs_data]") {
   // Yields duplicate index, but values are still zero, so both are
   // discarded and a warning is returned
   lp.a_matrix_.index_[0] = 0;
-  REQUIRE(highs.passModel(lp) == HighsStatus::kWarning);
+  REQUIRE(highs.passModel(lp) == HighsStatus::kOk);
 
   if (dev_run)
     printf("Give nonzero a_matrix_.value_[0] and a_matrix_.value_[1]\n");

check/TestRays.cpp

@@ -303,6 +303,8 @@ void testUnboundedMpsLp(const std::string model,
   // Test dual ray for unbounded LP
   model_file = std::string(HIGHS_DIR) + "/check/instances/" + model + ".mps";
   require_model_status = HighsModelStatus::kUnbounded;
+  // gas11 contains small nonzero matrix entries, so readModel yield
+  // HighsStatus::kWarning
   require_status = model == "gas11" ? HighsStatus::kWarning : HighsStatus::kOk;
   REQUIRE(highs.readModel(model_file) == require_status);
   REQUIRE(highs.changeObjectiveSense(sense) == HighsStatus::kOk);

src/lp_data/HighsSolve.cpp

@@ -127,7 +127,7 @@ HighsStatus solveLp(HighsLpSolverObject& solver_object, const string message) {
             return HighsStatus::kError;
           }
         }  // options.run_crossover == kHighsOnString
-      }    // unwelcome_ipx_status
+      }  // unwelcome_ipx_status
     } else {
       // PDLP has been used, so check whether claim of optimality
       // satisfies the HiGHS criteria

src/test/DevKkt.cpp

@@ -261,8 +261,8 @@ void checkComplementarySlackness(const State& state,
         if (fabs(state.colDual[i]) > tol &&
             fabs(state.colValue[i] - state.colUpper[i]) > tol) {
           if (dev_print)
-            std::cout << "Comp. slackness fail: "
-                      << "l[" << i << "]=" << state.colLower[i] << ", x[" << i
+            std::cout << "Comp. slackness fail: " << "l[" << i
+                      << "]=" << state.colLower[i] << ", x[" << i
                       << "]=" << state.colValue[i] << ", z[" << i
                       << "]=" << state.colDual[i] << std::endl;
           infeas = fabs(state.colDual[i]);

src/util/HighsMatrixUtils.cpp

@@ -234,13 +234,18 @@ HighsStatus assessMatrix(
       error_found = true;
       assert(num_small_values == 0);
     }
-    highsLogUser(log_options, HighsLogType::kWarning,
-                 "%s matrix packed vector contains %" HIGHSINT_FORMAT
-                 " |values| in [%g, %g] "
-                 "less than or equal to %g: ignored\n",
-                 matrix_name.c_str(), num_small_values, min_small_value,
-                 max_small_value, small_matrix_value);
-    warning_found = true;
+    // If explicit zeros are ignored, then no model information is
+    // lost, so only report and return a warning if small nonzeros are
+    // ignored
+    if (max_small_value > 0) {
+      highsLogUser(log_options, HighsLogType::kWarning,
+                   "%s matrix packed vector contains %" HIGHSINT_FORMAT
+                   " |values| in [%g, %g] "
+                   "less than or equal to %g: ignored\n",
+                   matrix_name.c_str(), num_small_values, min_small_value,
+                   max_small_value, small_matrix_value);
+      warning_found = true;
+    }
   }
   matrix_start[num_vec] = num_new_nz;
   HighsStatus return_status = HighsStatus::kOk;