Merge branch 'latest' into py-hipo

Author: galabovaa

check/TestIis.cpp

@@ -207,14 +207,23 @@ TEST_CASE("lp-get-iis", "[iis]") {
   highs.setOptionValue("output_flag", dev_run);
   highs.passModel(lp);
   HighsIis iis;
-  REQUIRE(highs.getIis(iis) == HighsStatus::kOk);
-  REQUIRE(highs.getModelStatus() == HighsModelStatus::kInfeasible);
-  REQUIRE(iis.col_index_.size() == 2);
-  REQUIRE(iis.row_index_.size() == 1);
-  REQUIRE(iis.col_index_[0] == 0);
-  REQUIRE(iis.col_index_[1] == 1);
-  REQUIRE(iis.row_index_[0] == 2);
-
+  const HighsLp& highs_lp = highs.getLp();
+  // First pass with incumbent matrix colwise; second with it
+  // rowwise
+  highs.ensureColwise();
+  REQUIRE(highs_lp.a_matrix_.isColwise());
+  for (HighsInt k = 0; k < 2; k++) {
+    REQUIRE(highs.getIis(iis) == HighsStatus::kOk);
+    REQUIRE(highs.getModelStatus() == HighsModelStatus::kInfeasible);
+    REQUIRE(iis.col_index_.size() == 2);
+    REQUIRE(iis.row_index_.size() == 1);
+    REQUIRE(iis.col_index_[0] == 0);
+    REQUIRE(iis.col_index_[1] == 1);
+    REQUIRE(iis.row_index_[0] == 2);
+    highs.clearSolver();
+    highs.ensureRowwise();
+    REQUIRE(highs_lp.a_matrix_.isRowwise());
+  }
   highs.resetGlobalScheduler(true);
 }
 
@@ -397,7 +406,7 @@ void testMps(std::string& model, const HighsInt iis_strategy,
   std::string model_file =
       std::string(HIGHS_DIR) + "/check/instances/" + model + ".mps";
   Highs highs;
-  highs.setOptionValue("output_flag", dev_run);
+  //  highs.setOptionValue("output_flag", dev_run);
 
   REQUIRE(highs.readModel(model_file) == HighsStatus::kOk);
   //  if (iis_strategy == kIisStrategyFromRayRowPriority ||

check/TestMipSolver.cpp

@@ -1279,3 +1279,16 @@ TEST_CASE("row-fixed-lp", "[highs_test_mip_solver]") {
 
   h.resetGlobalScheduler(true);
 }
+
+TEST_CASE("issue-2585", "[highs_test_mip_solver]") {
+  std::string filename =
+      std::string(HIGHS_DIR) + "/check/instances/issue-2585.lp";
+  Highs highs;
+  highs.setOptionValue("output_flag", dev_run);
+  highs.setOptionValue("mip_rel_gap", 0);
+  highs.setOptionValue("mip_abs_gap", 0);
+  highs.readModel(filename);
+  const HighsModelStatus require_model_status = HighsModelStatus::kOptimal;
+  const double optimal_objective = -175.91;
+  solve(highs, kHighsOnString, require_model_status, optimal_objective);
+}

check/instances/issue-2585.lp

@@ -0,0 +1,16 @@
+Minimize -24 a + 5 b + 7.4 c + 9 d
+Subject To
+96.55 a - 32.45 c + 88.78 d <= 1216.06
+-3.14 a - 78.02 b <= -50.5404
+11.8 b - 21.94 c <= 3.422
+91.59 c - 10.58 d <= -35.25
+79.17 a + 1.73 b - 73.23 d <= 411.403
+-10.61 a - 94.66 b + 76.88 d <= 195.69
+Bounds
+ -100 <= a <= 100
+ -100 <= b <= 100
+ -100 <= c <= 100
+ -100 <= d <= 100
+Generals
+c d
+End

cmake/sources.cmake

@@ -184,6 +184,7 @@ set(hipo_sources
     ipm/hipo/ipm/Iterate.cpp 
     ipm/hipo/ipm/LogHighs.cpp
     ipm/hipo/ipm/Model.cpp
+    ipm/hipo/ipm/Refine.cpp
     ipm/hipo/ipm/Solver.cpp)
 
 set(hipo_headers

docs/make.jl

@@ -2,9 +2,6 @@
 *                                                                       *
 *    This file is part of the HiGHS linear optimization suite           *
 *                                                                       *
-*    Written and engineered 2008-2024 by Julian Hall, Ivet Galabova,    *
-*    Leona Gottwald and Michael Feldmeier                               *
-*                                                                       *
 *    Available as open-source under the MIT License                     *
 *                                                                       *
 * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *=#
@@ -68,7 +65,8 @@ Documenter.makedocs(
                 "structures/classes/HighsSparseMatrix.md",
                 "structures/classes/HighsLp.md",
                 "structures/classes/HighsHessian.md",
-                "structures/classes/HighsModel.md"
+                "structures/classes/HighsModel.md",
+                "structures/classes/HighsIis.md"
             ],
 	    "Structures" => Any[
                 "structures/structs/index.md",

docs/src/guide/advanced.md

@@ -29,3 +29,34 @@ and
 yield a specific row or column of ``B^{-1}A``. In all cases,
 HiGHS can return the number and indices of the nonzeros in the result.
 
+## [Irreducible infeasibility system (IIS) detection](@id highs-iis)
+
+An Irreducible infeasibility system (IIS) consists of a set of
+variables and a set of constraints in a model, together with
+variable/constraint bound information, that cannot be satisfied (so is
+infeasible). It is irreducible in that if any constraint or variable
+bound is removed, then the system can be satisfied (so is feasible).
+
+HiGHS has an IIS facility that is under development. Currently it can
+only be used for LPs. The full IIS calculation is expensive, since it
+requires the solution of multiple LPs. Although there is a prototype
+implementation, it is not as robust or efficient as it will
+be. Otherwise, there is a simple, cheap test that looks for
+infeasibility due to incompatible variable oe constraint bounds, or
+constraint bounds that cannot be satisfied given the range of values
+on the constraint activity implied by bounds on variables.
+
+The choice of IIS strategy is defined by the [iis_strategy](@id option-iis-strategy) option, which can take the value
+
+- `kIisStrategyLight` = 0: The cheap test
+- `kIisStrategyFromLpRowPriority` = 1: The full IIS calculation, aiming to have a minimal number of rows in the IIS
+- `kIisStrategyFromLpColPriority` = 2: The full IIS calculation, aiming to have a minimal number of columns in the IIS
+
+### IIS-related methods in the `Highs` class
+
+- `const HighsLp& getIisLp()`: Return a const reference to the internal IIS LP instance
+- `HighsStatus getIis(HighsIis& iis)`: Try to find an IIS for the incumbent model. Gets the internal [HighsIis](@ref) instance, returning `HighsStatus::kError` if the calculation failed. Note that if the incumbent model is found to be feasible, this is a "success", and `HighsStatus::kOk` is returned.
+- ` HighsStatus writeIisModel(const std::string& filename = "")`: Write out the internal IIS LP instance to a file.
+
+
+

docs/src/guide/further.md

@@ -125,8 +125,8 @@ linear objective is represented by the following data, held in the
 
 Multi-objective optimization in HiGHS is defined by the following methods
 
-- [addLinearObjective](@ref Multi-objective-optimization] - Add a single `HighsLinearObjective` instance to any already stored in HiGHS
-- [clearLinearObjectives](@ref Multi-objective-optimization] - Clears any linear objectives stored in HiGHS
+- [addLinearObjective](@ref Multi-objective-optimization) - Add a single `HighsLinearObjective` instance to any already stored in HiGHS
+- [clearLinearObjectives](@ref Multi-objective-optimization) - Clears any linear objectives stored in HiGHS
 
 When there is at least one `HighsLinearObjective` instance in HiGHS,
 the `col_cost_` data in the incumbent model is ignored.

docs/src/installation.md

@@ -39,8 +39,8 @@ git checkout 521-ts
 
 Then build with
 ```
-cmake -S. -B build
--DGKLIB_PATH=/path_to_METIS_repo/GKlib
+cmake -S. -B build \
+-DGKLIB_PATH=/path_to_METIS_repo/GKlib \
 -DCMAKE_INSTALL_PREFIX=path_to_installs_dir
 cmake --build build
 cmake --install build

docs/src/options/definitions.md

@@ -486,7 +486,7 @@
 - Range: [0, inf]
 - Default: 1e-07
 
-## iis\_strategy
+## [iis\_strategy](@id option-iis-strategy)
 - Strategy for IIS calculation: Light test / Full and prioritise rows / Full and prioritise columns (0/1/2)
 - Type: integer
 - Range: {0, 2}

docs/src/structures/classes/HighsHessian.md

@@ -2,8 +2,8 @@
 
 A Hessian matrix is communicated via an instance of the HighsHessian class.
 
-- dim_: Scalar of type integer - Dimension of the Hessian
-- format\_: Scalar of [HessianFormat](@ref) type - Format of the Hessian
-- start\_: Vector of integer type - Start of each compressed column in the Hessian
-- index\_: Vector of integer type - Indices of the nonzeros in the Hessian
-- value\_: Vector of double type - Values of the nonzeros in the Hessian
+- `dim_`: Scalar of type integer - Dimension of the Hessian
+- `format_`: Scalar of [HessianFormat](@ref) type - Format of the Hessian
+- `start_`: Vector of integer type - Start of each compressed column in the Hessian
+- `index_`: Vector of integer type - Indices of the nonzeros in the Hessian
+- `value_`: Vector of double type - Values of the nonzeros in the Hessian