Enable user to write solution file in HiGHS

Author: metab0t

.gitignore

@@ -16,4 +16,5 @@ debug/
 docs/jupyter_execute
 docs/build
 
-*.lp
+*.lp
+*.sol

include/pyoptinterface/highs_model.hpp

@@ -14,6 +14,8 @@
 	B(Highs_create);                \
 	B(Highs_destroy);               \
 	B(Highs_writeModel);            \
+	B(Highs_writeSolution);         \
+	B(Highs_writeSolutionPretty);   \
 	B(Highs_addCol);                \
 	B(Highs_getNumCol);             \
 	B(Highs_changeColIntegrality);  \
@@ -112,7 +114,7 @@ class POIHighsModel
 	void init();
 	void close();
 
-	void write(const std::string &filename);
+	void write(const std::string &filename, bool pretty);
 
 	VariableIndex add_variable(VariableDomain domain = VariableDomain::Continuous,
 	                           double lb = -kHighsInf, double ub = kHighsInf,

lib/highs_model.cpp

@@ -119,9 +119,25 @@ void POIHighsModel::close()
 	m_model.reset();
 }
 
-void POIHighsModel::write(const std::string &filename)
+void POIHighsModel::write(const std::string &filename, bool pretty)
 {
-	auto error = highs::Highs_writeModel(m_model.get(), filename.c_str());
+	bool is_solution = false;
+	if (filename.ends_with(".sol"))
+	{
+		is_solution = true;
+	}
+	HighsInt error;
+	if (is_solution)
+	{
+		if (pretty)
+			error = highs::Highs_writeSolutionPretty(m_model.get(), filename.c_str());
+		else
+			error = highs::Highs_writeSolution(m_model.get(), filename.c_str());
+	}
+	else
+	{
+		error = highs::Highs_writeModel(m_model.get(), filename.c_str());
+	}
 	check_error(error);
 }
 

lib/highs_model_ext.cpp

@@ -39,9 +39,9 @@ NB_MODULE(highs_model_ext, m)
 	    .def_ro("m_n_constraints", &HighsModelMixin::m_n_constraints)
 	    // clang-format off
 	    BIND_F(init)
-	    BIND_F(write)
 	    BIND_F(close)
 	    // clang-format on
+	    .def("write", &HighsModelMixin::write, nb::arg("filename"), nb::arg("pretty") = false)
 
 	    .def_ro("solution", &HighsModelMixin::m_solution)
 

lib/mosek_model.cpp

@@ -184,7 +184,7 @@ void MOSEKModel::close()
 void MOSEKModel::write(const std::string &filename)
 {
 	bool is_solution = false;
-	if (filename.ends_with(".sol") || filename.ends_with(".bas") || filename.ends_with("int"))
+	if (filename.ends_with(".sol") || filename.ends_with(".bas") || filename.ends_with(".int"))
 	{
 		is_solution = true;
 	}

tests/highs_writefile.py

@@ -0,0 +1,13 @@
+import pyoptinterface as poi
+from pyoptinterface import highs
+
+model = highs.Model()
+
+x = model.add_m_variables(10, lb=0.0, ub=10.0)
+model.add_linear_constraint(poi.quicksum(x) >= 20.0)
+
+model.set_objective(poi.quicksum(v * v for v in x))
+model.optimize()
+
+model.write("highs_test.sol")
+model.write("highs_test_pretty.sol", pretty=True)