InternalSolver: set_constraint_sense, set_constraint_rhs

miplearn/solvers/gurobi.py

@@ -274,6 +274,14 @@ class GurobiSolver(InternalSolver):
     def get_constraint_slacks(self):
         return {c.ConstrName: c.Slack for c in self.model.getConstrs()}
 
+    def set_constraint_sense(self, cid, sense):
+        c = self.model.getConstrByName(cid)
+        c.Sense = sense
+
+    def set_constraint_rhs(self, cid, rhs):
+        c = self.model.getConstrByName(cid)
+        c.RHS = rhs
+
     def relax(self):
         self.model = self.model.relax()
         self._update_vars()

miplearn/solvers/internal.py

@@ -195,6 +195,14 @@ class InternalSolver(ABC):
     def is_constraint_satisfied(self, cobj):
         pass
 
+    @abstractmethod
+    def set_constraint_sense(self, cid, sense):
+        pass
+
+    @abstractmethod
+    def set_constraint_rhs(self, cid, rhs):
+        pass
+
     @abstractmethod
     def set_threads(self, threads):
         pass

miplearn/solvers/pyomo/base.py

@@ -219,12 +219,6 @@ class BasePyomoSolver(InternalSolver):
     def get_constraint_ids(self):
         return list(self._cname_to_constr.keys())
 
-    def extract_constraint(self, cid):
-        raise Exception("Not implemented")
-
-    def is_constraint_satisfied(self, cobj):
-        raise Exception("Not implemented")
-
     @abstractmethod
     def _get_warm_start_regexp(self):
         pass
@@ -249,8 +243,20 @@ class BasePyomoSolver(InternalSolver):
     def _get_gap_tolerance_option_name(self):
         pass
 
+    def extract_constraint(self, cid):
+        raise Exception("Not implemented")
+
+    def is_constraint_satisfied(self, cobj):
+        raise Exception("Not implemented")
+
     def relax(self):
         raise Exception("not implemented")
 
     def get_constraint_slacks(self):
         raise Exception("not implemented")
+
+    def set_constraint_sense(self, cid, sense):
+        raise Exception("Not implemented")
+
+    def set_constraint_rhs(self, cid, rhs):
+        raise Exception("Not implemented")

miplearn/solvers/tests/test_internal_solver.py

@@ -122,7 +122,7 @@ def test_internal_solver():
         assert stats["Lower bound"] == 1030.0
 
         if isinstance(solver, GurobiSolver):
-            # Extract new constraint
+            # Extract the new constraint
             cobj = solver.extract_constraint("cut")
 
             # New constraint should no longer affect solution and should no longer
@@ -145,6 +145,13 @@ def test_internal_solver():
             # New constraint should now be satisfied
             assert solver.is_constraint_satisfied(cobj)
 
+            # Relax problem and make cut into an equality constraint
+            solver.relax()
+            solver.set_constraint_rhs("cut", 0.5)
+            solver.set_constraint_sense("cut", "=")
+            stats = solver.solve()
+            assert round(stats["Lower bound"]) == 1179.0
+
 
 def test_iteration_cb():
     for solver_class in _get_internal_solvers():