Merge pull request #2 from Doing-The-Math/rs/highs_fixes

Rs/highs fixes

Author: rschwarz

mip/highs.py

@@ -720,7 +720,7 @@ def __init__(self, model: mip.Model, name: str, sense: str):
         # Buffer string for storing names
         self._name_buffer = ffi.new(f"char[{self._lib.kHighsMaximumStringLength}]")
 
-        # type conversion maps
+        # type conversion maps (can not distinguish binary from integer!)
         self._var_type_map = {
             mip.CONTINUOUS: self._lib.kHighsVarTypeContinuous,
             mip.BINARY: self._lib.kHighsVarTypeInteger,
@@ -760,8 +760,8 @@ def _get_double_option_value(self: "SolverHighs", name: str) -> float:
         )
         return value[0]
 
-    def _get_bool_option_value(self: "SolverHighs", name: str) -> float:
-        value = ffi.new("bool*")
+    def _get_bool_option_value(self: "SolverHighs", name: str) -> int:
+        value = ffi.new("int*")
         check(
             self._lib.Highs_getBoolOptionValue(self._model, name.encode("UTF-8"), value)
         )
@@ -779,7 +779,7 @@ def _set_double_option_value(self: "SolverHighs", name: str, value: float):
             )
         )
 
-    def _set_bool_option_value(self: "SolverHighs", name: str, value: float):
+    def _set_bool_option_value(self: "SolverHighs", name: str, value: int):
         check(
             self._lib.Highs_setBoolOptionValue(self._model, name.encode("UTF-8"), value)
         )
@@ -815,6 +815,8 @@ def add_var(
         if name:
             check(self._lib.Highs_passColName(self._model, col, name.encode("utf-8")))
         if var_type != mip.CONTINUOUS:
+            # Note that HiGHS doesn't distinguish binary and integer variables
+            # by type. There is only a boolean flag for "integrality".
             self._num_int_vars += 1
             check(
                 self._lib.Highs_changeColIntegrality(
@@ -1035,6 +1037,18 @@ def set_start(self: "SolverHighs", start: List[Tuple["mip.Var", numbers.Real]]):
         self._lib.Highs_setSolution(self._model, cval, ffi.NULL, ffi.NULL, ffi.NULL)
 
     def set_objective(self: "SolverHighs", lin_expr: "mip.LinExpr", sense: str = ""):
+        # first reset old objective (all 0)
+        n = self.num_cols()
+        costs = ffi.new("double[]", n)  # initialized to 0
+        check(
+            self._lib.Highs_changeColsCostByRange(
+                self._model,
+                0,  # from_col
+                n - 1,  # to_col
+                costs,
+            )
+        )
+
         # set coefficients
         for var, coef in lin_expr.expr.items():
             check(self._lib.Highs_changeColCost(self._model, var.idx, coef))
@@ -1518,7 +1532,11 @@ def remove_vars(self: "SolverHighs", varsList: List[int]):
 
     def var_get_index(self: "SolverHighs", name: str) -> int:
         idx = ffi.new("int *")
-        self._lib.Highs_getColByName(self._model, name.encode("utf-8"), idx)
+        status = self._lib.Highs_getColByName(self._model, name.encode("utf-8"), idx)
+        if status == STATUS_ERROR:
+            # This means that no var with that name was found. Unfortunately,
+            # HiGHS::getColByName doesn't assign a value to idx in that case.
+            return -1
         return idx[0]
 
     def get_problem_name(self: "SolverHighs") -> str:

test/mip_files_test.py

@@ -139,6 +139,9 @@ def test_mip_file(solver: str, instance: str):
 
     max_dif = max(max(abs(ub), abs(lb)) * 0.01, TOL)
 
+    if solver == HIGHS and instance.endswith(".gz"):
+        pytest.skip("HiGHS does not support .gz files.")
+
     m.read(instance)
     if bas_file:
        m.verbose = True

test/mip_test.py

@@ -556,11 +556,21 @@ def test_constr_by_name_rhs(self, solver):
         assert model.constr_by_name("row0").rhs == val
 
     @pytest.mark.parametrize("solver", SOLVERS)
-    def test_var_by_name_rhs(self, solver):
+    def test_var_by_name_valid(self, solver):
         n, model = self.build_model(solver)
 
-        v = model.var_by_name("x({},{})".format(0, 0))
+        name = "x({},{})".format(0, 0)
+        v = model.var_by_name(name)
         assert v is not None
+        assert isinstance(v, mip.Var)
+        assert v.name == name
+
+    @pytest.mark.parametrize("solver", SOLVERS)
+    def test_var_by_name_invalid(self, solver):
+        n, model = self.build_model(solver)
+
+        v = model.var_by_name("xyz_invalid_name")
+        assert v is None
 
     @pytest.mark.parametrize("solver", SOLVERS)
     def test_obj_const1(self, solver: str):

test/test_model.py

@@ -1294,6 +1294,21 @@ def test_copy(solver):
     assert id(term.expr) != id(term_copy.expr)
 
 
+@skip_on(NotImplementedError)
+@pytest.mark.parametrize("solver", SOLVERS)
+def test_verbose(solver):
+    # set and get verbose flag
+    m = Model(solver_name=solver)
+
+    # active
+    m.verbose = 1
+    assert m.verbose == 1
+
+    # inactive
+    m.verbose = 0
+    assert m.verbose == 0
+
+
 @skip_on(NotImplementedError)
 @pytest.mark.parametrize("solver", SOLVERS)
 def test_constraint_with_lin_expr_and_lin_expr(solver):
@@ -1356,6 +1371,7 @@ def test_objective(solver):
     m = Model(solver_name=solver, sense=MAXIMIZE)
     x = m.add_var(name="x", lb=0, ub=1)
     y = m.add_var(name="y", lb=0, ub=1)
+    z = m.add_var(name="z", lb=0, ub=1)
 
     m.objective = x - y + 0.5
     assert m.objective.x is None
@@ -1374,13 +1390,13 @@ def test_objective(solver):
 
 
     # Test changing the objective
-    m.objective = x + y + 1.5
+    m.objective = y + 2*z + 1.5
     m.sense = MINIMIZE
     # TODO: assert m.objective.sense == MINIMIZE
 
     assert len(m.objective.expr) == 2
-    assert m.objective.expr[x] == 1
     assert m.objective.expr[y] == 1
+    assert m.objective.expr[z] == 2
     assert m.objective.const == 1.5
 
     status = m.optimize()