Redesign InternalSolver constraint methods

miplearn/components/dynamic_lazy.py

@@ -76,6 +76,7 @@ class DynamicLazyConstraintsComponent(Component):
         instance: Instance,
         model: Any,
     ) -> bool:
+        assert solver.internal_solver is not None
         logger.debug("Finding violated lazy constraints...")
         cids = instance.find_violated_lazy_constraints(solver.internal_solver, model)
         if len(cids) == 0:

miplearn/components/dynamic_user_cuts.py

@@ -53,8 +53,7 @@ class UserCutsComponent(Component):
         cids = self.dynamic.sample_predict(instance, training_data)
         logger.info("Enforcing %d user cuts ahead-of-time..." % len(cids))
         for cid in cids:
-            cobj = instance.build_user_cut(model, cid)
-            solver.internal_solver.add_constraint(cobj)
+            instance.enforce_user_cut(solver.internal_solver, model, cid)
         stats["UserCuts: Added ahead-of-time"] = len(cids)
 
     @overrides
@@ -73,9 +72,7 @@ class UserCutsComponent(Component):
             if cid in self.enforced:
                 continue
             assert isinstance(cid, Hashable)
-            cobj = instance.build_user_cut(model, cid)
-            assert cobj is not None
-            solver.internal_solver.add_cut(cobj)
+            instance.enforce_user_cut(solver.internal_solver, model, cid)
             self.enforced.add(cid)
             self.n_added_in_callback += 1
         if len(cids) > 0:

miplearn/components/static_lazy.py

@@ -12,7 +12,7 @@ from miplearn.classifiers import Classifier
 from miplearn.classifiers.counting import CountingClassifier
 from miplearn.classifiers.threshold import MinProbabilityThreshold, Threshold
 from miplearn.components.component import Component
-from miplearn.features import TrainingSample, Features
+from miplearn.features import TrainingSample, Features, Constraint
 from miplearn.types import LearningSolveStats
 
 logger = logging.getLogger(__name__)
@@ -44,7 +44,7 @@ class StaticLazyConstraintsComponent(Component):
         self.threshold_prototype: Threshold = threshold
         self.classifiers: Dict[Hashable, Classifier] = {}
         self.thresholds: Dict[Hashable, Threshold] = {}
-        self.pool: Dict[str, LazyConstraint] = {}
+        self.pool: Dict[str, Constraint] = {}
         self.violation_tolerance: float = violation_tolerance
         self.enforced_cids: Set[Hashable] = set()
         self.n_restored: int = 0
@@ -72,10 +72,8 @@ class StaticLazyConstraintsComponent(Component):
         self.pool = {}
         for (cid, cdict) in features.constraints.items():
             if cdict.lazy and cid not in self.enforced_cids:
-                self.pool[cid] = LazyConstraint(
-                    cid=cid,
-                    obj=solver.internal_solver.extract_constraint(cid),
-                )
+                self.pool[cid] = cdict
+                solver.internal_solver.remove_constraint(cid)
         logger.info(
             f"{len(self.enforced_cids)} lazy constraints kept; "
             f"{len(self.pool)} moved to the pool"
@@ -124,18 +122,18 @@ class StaticLazyConstraintsComponent(Component):
     def _check_and_add(self, solver: "LearningSolver") -> bool:
         assert solver.internal_solver is not None
         logger.info("Finding violated lazy constraints...")
-        enforced: List[LazyConstraint] = []
+        enforced: Dict[str, Constraint] = {}
         for (cid, c) in self.pool.items():
             if not solver.internal_solver.is_constraint_satisfied(
-                c.obj,
+                c,
                 tol=self.violation_tolerance,
             ):
-                enforced.append(c)
+                enforced[cid] = c
         logger.info(f"{len(enforced)} violations found")
-        for c in enforced:
-            del self.pool[c.cid]
-            solver.internal_solver.add_constraint(c.obj)
-            self.enforced_cids.add(c.cid)
+        for (cid, c) in enforced.items():
+            del self.pool[cid]
+            solver.internal_solver.add_constraint(c, name=cid)
+            self.enforced_cids.add(cid)
             self.n_restored += 1
         logger.info(
             f"{len(enforced)} constraints restored; {len(self.pool)} in the pool"

miplearn/instance/base.py

@@ -16,6 +16,7 @@ logger = logging.getLogger(__name__)
 if TYPE_CHECKING:
     from miplearn.solvers.learning import InternalSolver
 
+
 # noinspection PyMethodMayBeStatic
 class Instance(ABC, EnforceOverrides):
     """
@@ -170,7 +171,12 @@ class Instance(ABC, EnforceOverrides):
     def find_violated_user_cuts(self, model: Any) -> List[Hashable]:
         return []
 
-    def build_user_cut(self, model: Any, violation: Hashable) -> Any:
+    def enforce_user_cut(
+        self,
+        solver: "InternalSolver",
+        model: Any,
+        violation: Hashable,
+    ) -> Any:
         return None
 
     def load(self) -> None:

miplearn/instance/picklegz.py

@@ -106,9 +106,14 @@ class PickleGzInstance(Instance):
         return self.instance.find_violated_user_cuts(model)
 
     @overrides
-    def build_user_cut(self, model: Any, violation: Hashable) -> None:
+    def enforce_user_cut(
+        self,
+        solver: "InternalSolver",
+        model: Any,
+        violation: Hashable,
+    ) -> None:
         assert self.instance is not None
-        self.instance.build_user_cut(model, violation)
+        self.instance.enforce_user_cut(solver, model, violation)
 
     @overrides
     def load(self) -> None:

miplearn/problems/tsp.py

@@ -11,7 +11,7 @@ from scipy.spatial.distance import pdist, squareform
 from scipy.stats import uniform, randint
 from scipy.stats.distributions import rv_frozen
 
-from miplearn import InternalSolver
+from miplearn import InternalSolver, BasePyomoSolver
 from miplearn.instance.base import Instance
 from miplearn.types import VariableName, Category
 
@@ -108,14 +108,15 @@ class TravelingSalesmanInstance(Instance):
         model: Any,
         component: FrozenSet,
     ) -> None:
+        assert isinstance(solver, BasePyomoSolver)
         cut_edges = [
             e
             for e in self.edges
             if (e[0] in component and e[1] not in component)
             or (e[0] not in component and e[1] in component)
         ]
-        constr = model.eq_subtour.add(sum(model.x[e] for e in cut_edges) >= 2)
-        solver.add_constraint(constr)
+        constr = model.eq_subtour.add(expr=sum(model.x[e] for e in cut_edges) >= 2)
+        solver.add_constraint(constr, name="")
 
 
 class TravelingSalesmanGenerator:

miplearn/solvers/gurobi.py

@@ -32,14 +32,6 @@ from miplearn.types import (
 logger = logging.getLogger(__name__)
 
 
-@dataclass
-class ExtractedGurobiConstraint:
-    lhs: Any
-    rhs: float
-    sense: str
-    name: str
-
-
 class GurobiSolver(InternalSolver):
     """
     An InternalSolver backed by Gurobi's Python API (without Pyomo).
@@ -72,10 +64,10 @@ class GurobiSolver(InternalSolver):
         self.instance: Optional[Instance] = None
         self.model: Optional["gurobipy.Model"] = None
         self.params: SolverParams = params
-        self.varname_to_var: Dict[str, "gurobipy.Var"] = {}
-        self.bin_vars: List["gurobipy.Var"] = []
         self.cb_where: Optional[int] = None
         self.lazy_cb_frequency = lazy_cb_frequency
+        self._bin_vars: List["gurobipy.Var"] = []
+        self._varname_to_var: Dict[str, "gurobipy.Var"] = {}
 
         if self.lazy_cb_frequency == 1:
             self.lazy_cb_where = [self.gp.GRB.Callback.MIPSOL]
@@ -106,20 +98,20 @@ class GurobiSolver(InternalSolver):
 
     def _update_vars(self) -> None:
         assert self.model is not None
-        self.varname_to_var.clear()
-        self.bin_vars.clear()
+        self._varname_to_var.clear()
+        self._bin_vars.clear()
         for var in self.model.getVars():
-            assert var.varName not in self.varname_to_var, (
+            assert var.varName not in self._varname_to_var, (
                 f"Duplicated variable name detected: {var.varName}. "
                 f"Unique variable names are currently required."
             )
-            self.varname_to_var[var.varName] = var
+            self._varname_to_var[var.varName] = var
             assert var.vtype in ["B", "C"], (
                 "Only binary and continuous variables are currently supported. "
                 "Variable {var.varName} has type {var.vtype}."
             )
             if var.vtype == "B":
-                self.bin_vars.append(var)
+                self._bin_vars.append(var)
 
     def _apply_params(self, streams: List[Any]) -> None:
         assert self.model is not None
@@ -138,13 +130,13 @@ class GurobiSolver(InternalSolver):
             streams += [sys.stdout]
         self._apply_params(streams)
         assert self.model is not None
-        for var in self.bin_vars:
+        for var in self._bin_vars:
             var.vtype = self.gp.GRB.CONTINUOUS
             var.lb = 0.0
             var.ub = 1.0
         with _RedirectOutput(streams):
             self.model.optimize()
-        for var in self.bin_vars:
+        for var in self._bin_vars:
             var.vtype = self.gp.GRB.BINARY
         log = streams[0].getvalue()
         opt_value = None
@@ -262,7 +254,7 @@ class GurobiSolver(InternalSolver):
         self._raise_if_callback()
         self._clear_warm_start()
         for (var_name, value) in solution.items():
-            var = self.varname_to_var[var_name]
+            var = self._varname_to_var[var_name]
             if value is not None:
                 var.start = value
 
@@ -288,16 +280,13 @@ class GurobiSolver(InternalSolver):
         else:
             return c.pi
 
-    def _get_value(self, var: Any) -> Optional[float]:
+    def _get_value(self, var: Any) -> float:
         assert self.model is not None
         if self.cb_where == self.gp.GRB.Callback.MIPSOL:
             return self.model.cbGetSolution(var)
         elif self.cb_where == self.gp.GRB.Callback.MIPNODE:
             return self.model.cbGetNodeRel(var)
         elif self.cb_where is None:
-            if self.is_infeasible():
-                return None
-            else:
             return var.x
         else:
             raise Exception(
@@ -305,35 +294,40 @@ class GurobiSolver(InternalSolver):
             )
 
     @overrides
-    def add_constraint(self, cobj: Any, name: str = "") -> None:
+    def add_constraint(self, constr: Constraint, name: str) -> None:
         assert self.model is not None
-        if isinstance(cobj, ExtractedGurobiConstraint):
-            if self.cb_where in [
-                self.gp.GRB.Callback.MIPSOL,
-                self.gp.GRB.Callback.MIPNODE,
-            ]:
-                self.model.cbLazy(cobj.lhs, cobj.sense, cobj.rhs)
-            else:
-                self.model.addConstr(cobj.lhs, cobj.sense, cobj.rhs, cobj.name)
-        elif isinstance(cobj, self.gp.TempConstr):
-            if self.cb_where in [
-                self.gp.GRB.Callback.MIPSOL,
-                self.gp.GRB.Callback.MIPNODE,
-            ]:
-                self.model.cbLazy(cobj)
-            else:
-                self.model.addConstr(cobj, name=name)
+        lhs = self.gp.quicksum(
+            self._varname_to_var[varname] * coeff
+            for (varname, coeff) in constr.lhs.items()
+        )
+        if constr.sense == "=":
+            self.model.addConstr(lhs == constr.rhs, name=name)
+        elif constr.sense == "<":
+            self.model.addConstr(lhs <= constr.rhs, name=name)
         else:
-            raise Exception(f"unknown constraint type: {cobj.__class__.__name__}")
+            self.model.addConstr(lhs >= constr.rhs, name=name)
 
     @overrides
-    def add_cut(self, cobj: Any) -> None:
+    def remove_constraint(self, name: str) -> None:
         assert self.model is not None
-        assert self.cb_where == self.gp.GRB.Callback.MIPNODE
-        self.model.cbCut(cobj)
+        constr = self.model.getConstrByName(name)
+        self.model.remove(constr)
+
+    @overrides
+    def is_constraint_satisfied(self, constr: Constraint, tol: float = 1e-6) -> bool:
+        lhs = 0.0
+        for (varname, coeff) in constr.lhs.items():
+            var = self._varname_to_var[varname]
+            lhs += self._get_value(var) * coeff
+        if constr.sense == "<":
+            return lhs <= constr.rhs + tol
+        elif constr.sense == ">":
+            return lhs >= constr.rhs - tol
+        else:
+            return abs(constr.rhs - lhs) < abs(tol)
 
     def _clear_warm_start(self) -> None:
-        for var in self.varname_to_var.values():
+        for var in self._varname_to_var.values():
             var.start = self.gp.GRB.UNDEFINED
 
     @overrides
@@ -342,50 +336,11 @@ class GurobiSolver(InternalSolver):
         for (varname, value) in solution.items():
             if value is None:
                 continue
-            var = self.varname_to_var[varname]
+            var = self._varname_to_var[varname]
             var.vtype = self.gp.GRB.CONTINUOUS
             var.lb = value
             var.ub = value
 
-    @overrides
-    def extract_constraint(self, cid: str) -> ExtractedGurobiConstraint:
-        self._raise_if_callback()
-        assert self.model is not None
-        constr = self.model.getConstrByName(cid)
-        cobj = ExtractedGurobiConstraint(
-            lhs=self.model.getRow(constr),
-            sense=constr.sense,
-            rhs=constr.RHS,
-            name=constr.ConstrName,
-        )
-        self.model.remove(constr)
-        return cobj
-
-    @overrides
-    def is_constraint_satisfied(
-        self,
-        cobj: ExtractedGurobiConstraint,
-        tol: float = 1e-6,
-    ) -> bool:
-        assert isinstance(cobj, ExtractedGurobiConstraint)
-        lhs, sense, rhs, _ = cobj.lhs, cobj.sense, cobj.rhs, cobj.name
-        if self.cb_where is not None:
-            lhs_value = lhs.getConstant()
-            for i in range(lhs.size()):
-                var = lhs.getVar(i)
-                coeff = lhs.getCoeff(i)
-                lhs_value += self._get_value(var) * coeff
-        else:
-            lhs_value = lhs.getValue()
-        if sense == "<":
-            return lhs_value <= rhs + tol
-        elif sense == ">":
-            return lhs_value >= rhs - tol
-        elif sense == "=":
-            return abs(rhs - lhs_value) < abs(tol)
-        else:
-            raise Exception("Unknown sense: %s" % sense)
-
     @overrides
     def get_inequality_slacks(self) -> Dict[str, float]:
         assert self.model is not None
@@ -545,4 +500,5 @@ class GurobiTestInstanceKnapsack(PyomoTestInstanceKnapsack):
         model: Any,
         violation: Hashable,
     ) -> None:
-        solver.add_constraint(model.getVarByName("x[0]") <= 0, name="cut")
+        x0 = model.getVarByName("x[0]")
+        model.cbLazy(x0 <= 0)

miplearn/solvers/internal.py

@@ -6,6 +6,8 @@ import logging
 from abc import ABC, abstractmethod
 from typing import Any, Dict, List, Optional
 
+from overrides import EnforceOverrides
+
 from miplearn.features import Constraint
 from miplearn.instance.base import Instance
 from miplearn.types import (
@@ -22,7 +24,7 @@ from miplearn.types import (
 logger = logging.getLogger(__name__)
 
 
-class InternalSolver(ABC):
+class InternalSolver(ABC, EnforceOverrides):
     """
     Abstract class representing the MIP solver used internally by LearningSolver.
     """
@@ -155,31 +157,21 @@ class InternalSolver(ABC):
         pass
 
     @abstractmethod
-    def add_constraint(self, cobj: Any, name: str = "") -> None:
+    def add_constraint(self, constr: Constraint, name: str) -> None:
         """
-        Adds a single constraint to the model.
+        Adds a given constraint to the model.
         """
         pass
 
-    def add_cut(self, cobj: Any) -> None:
-        """
-        Adds a cutting plane to the model. This function can only be called from a user
-        cut callback.
-        """
-        raise NotImplementedError()
-
     @abstractmethod
-    def extract_constraint(self, cid: str) -> Any:
+    def remove_constraint(self, name: str) -> None:
         """
-        Removes a given constraint from the model and returns an object `cobj` which
-        can be used to verify if the removed constraint is still satisfied by
-        the current solution, using `is_constraint_satisfied(cobj)`, and can potentially
-        be re-added to the model using `add_constraint(cobj)`.
+        Removes the constraint that has a given name from the model.
         """
         pass
 
     @abstractmethod
-    def is_constraint_satisfied(self, cobj: Any, tol: float = 1e-6) -> bool:
+    def is_constraint_satisfied(self, constr: Constraint, tol: float = 1e-6) -> bool:
         """
         Returns True if the current solution satisfies the given constraint.
         """

miplearn/solvers/pyomo/base.py

@@ -6,14 +6,15 @@ import logging
 import re
 import sys
 from io import StringIO
-from typing import Any, List, Dict, Optional, Hashable
+from typing import Any, List, Dict, Optional
 
+import numpy as np
 import pyomo
 from overrides import overrides
 from pyomo import environ as pe
 from pyomo.core import Var
 from pyomo.core.base import _GeneralVarData
-from pyomo.core.base.constraint import SimpleConstraint, ConstraintList
+from pyomo.core.base.constraint import ConstraintList
 from pyomo.core.expr.numeric_expr import SumExpression, MonomialTermExpression
 from pyomo.opt import TerminationCondition
 from pyomo.opt.base.solvers import SolverFactory
@@ -35,7 +36,6 @@ from miplearn.types import (
     VariableName,
     Category,
 )
-import numpy as np
 
 logger = logging.getLogger(__name__)
 
@@ -215,7 +215,7 @@ class BasePyomoSolver(InternalSolver):
 
     def _update_constrs(self) -> None:
         assert self.model is not None
-        self._cname_to_constr = {}
+        self._cname_to_constr.clear()
         for constr in self.model.component_objects(pyomo.core.Constraint):
             if isinstance(constr, pe.ConstraintList):
                 for idx in constr:
@@ -233,24 +233,50 @@ class BasePyomoSolver(InternalSolver):
             self._pyomo_solver.update_var(var)
 
     @overrides
-    def add_constraint(self, cobj: Any, name: str = "") -> Any:
+    def add_constraint(
+        self,
+        constr: Any,
+        name: str,
+    ) -> None:
         assert self.model is not None
-        if isinstance(cobj, Constraint):
+        if isinstance(constr, Constraint):
             lhs = 0.0
-            for (varname, coeff) in cobj.lhs.items():
+            for (varname, coeff) in constr.lhs.items():
                 var = self._varname_to_var[varname]
                 lhs += var * coeff
-            if cobj.sense == "=":
-                expr = lhs == cobj.rhs
-            elif cobj.sense == "<":
-                expr = lhs <= cobj.rhs
+            if constr.sense == "=":
+                expr = lhs == constr.rhs
+            elif constr.sense == "<":
+                expr = lhs <= constr.rhs
             else:
-                expr = lhs >= cobj.rhs
-            cl = self.model.extra_constraints
-            self._pyomo_solver.add_constraint(cl.add(expr))
+                expr = lhs >= constr.rhs
+            cl = pe.Constraint(expr=expr, name=name)
+            self.model.add_component(name, cl)
+            self._pyomo_solver.add_constraint(cl)
+            self._cname_to_constr[name] = cl
         else:
-            self._pyomo_solver.add_constraint(cobj)
-        self._update_constrs()
+            self._pyomo_solver.add_constraint(constr)
+
+    @overrides
+    def remove_constraint(self, name: str) -> None:
+        assert self.model is not None
+        constr = self._cname_to_constr[name]
+        del self._cname_to_constr[name]
+        self.model.del_component(constr)
+        self._pyomo_solver.remove_constraint(constr)
+
+    @overrides
+    def is_constraint_satisfied(self, constr: Constraint, tol: float = 1e-6) -> bool:
+        lhs = 0.0
+        for (varname, coeff) in constr.lhs.items():
+            var = self._varname_to_var[varname]
+            lhs += var.value * coeff
+        if constr.sense == "<":
+            return lhs <= constr.rhs + tol
+        elif constr.sense == ">":
+            return lhs >= constr.rhs - tol
+        else:
+            return abs(constr.rhs - lhs) < abs(tol)
 
     @staticmethod
     def __extract(
@@ -304,27 +330,6 @@ class BasePyomoSolver(InternalSolver):
             result[cname] = cobj.slack()
         return result
 
-    @overrides
-    def extract_constraint(self, cid: str) -> Any:
-        cobj = self._cname_to_constr[cid]
-        constr = self._parse_pyomo_constraint(cobj)
-        self._pyomo_solver.remove_constraint(cobj)
-        return constr
-
-    @overrides
-    def is_constraint_satisfied(self, cobj: Any, tol: float = 1e-6) -> bool:
-        assert isinstance(cobj, Constraint)
-        lhs_value = 0.0
-        for (varname, coeff) in cobj.lhs.items():
-            var = self._varname_to_var[varname]
-            lhs_value += var.value * coeff
-        if cobj.sense == "=":
-            return (lhs_value <= cobj.rhs + tol) and (lhs_value >= cobj.rhs - tol)
-        elif cobj.sense == "<":
-            return lhs_value <= cobj.rhs + tol
-        else:
-            return lhs_value >= cobj.rhs - tol
-
     @overrides
     def is_infeasible(self) -> bool:
         return self._termination_condition == TerminationCondition.infeasible
@@ -411,6 +416,7 @@ class BasePyomoSolver(InternalSolver):
             sense=sense,
         )
 
+    @overrides
     def are_callbacks_supported(self) -> bool:
         return False
 
@@ -483,13 +489,3 @@ class PyomoTestInstanceKnapsack(Instance):
             self.weights[item],
             self.prices[item],
         ]
-
-    @overrides
-    def enforce_lazy_constraint(
-        self,
-        solver: InternalSolver,
-        model: Any,
-        violation: Hashable,
-    ) -> None:
-        model.cut = pe.Constraint(expr=model.x[0] <= 0.0, name="cut")
-        solver.add_constraint(model.cut)

miplearn/solvers/tests/__init__.py

@@ -75,39 +75,29 @@ def run_basic_usage_tests(solver: InternalSolver) -> None:
         solver.get_constraints(),
         {
             "eq_capacity": Constraint(
-                lhs={
-                    "x[0]": 23.0,
-                    "x[1]": 26.0,
-                    "x[2]": 20.0,
-                    "x[3]": 18.0,
-                },
+                lhs={"x[0]": 23.0, "x[1]": 26.0, "x[2]": 20.0, "x[3]": 18.0},
                 rhs=67.0,
                 sense="<",
             ),
         },
     )
 
-    # Add a brand new constraint
-    instance.enforce_lazy_constraint(solver, model, "cut")
+    # Build a new constraint
+    cut = Constraint(lhs={"x[0]": 1.0}, sense="<", rhs=0.0)
+    assert not solver.is_constraint_satisfied(cut)
 
-    # New constraint should be listed
+    # Add new constraint and verify that it is listed
+    solver.add_constraint(cut, "cut")
     assert_equals(
         solver.get_constraints(),
         {
             "eq_capacity": Constraint(
-                lhs={
-                    "x[0]": 23.0,
-                    "x[1]": 26.0,
-                    "x[2]": 20.0,
-                    "x[3]": 18.0,
-                },
+                lhs={"x[0]": 23.0, "x[1]": 26.0, "x[2]": 20.0, "x[3]": 18.0},
                 rhs=67.0,
                 sense="<",
             ),
             "cut": Constraint(
-                lhs={
-                    "x[0]": 1.0,
-                },
+                lhs={"x[0]": 1.0},
                 rhs=0.0,
                 sense="<",
             ),
@@ -117,35 +107,23 @@ def run_basic_usage_tests(solver: InternalSolver) -> None:
     # New constraint should affect the solution
     stats = solver.solve()
     assert_equals(stats["Lower bound"], 1030.0)
+    assert solver.is_constraint_satisfied(cut)
 
     # Verify slacks
     assert_equals(
         solver.get_inequality_slacks(),
-        {
-            "cut": 0.0,
-            "eq_capacity": 3.0,
-        },
+        {"cut": 0.0, "eq_capacity": 3.0},
     )
 
-    # # Extract the new constraint
-    cobj = solver.extract_constraint("cut")
+    # Remove the new constraint
+    solver.remove_constraint("cut")
 
     # New constraint should no longer affect solution
     stats = solver.solve()
     assert_equals(stats["Lower bound"], 1183.0)
 
-    # New constraint should not be satisfied by current solution
-    assert not solver.is_constraint_satisfied(cobj)
-
-    # Re-add constraint
-    solver.add_constraint(cobj)
-
-    # Constraint should affect solution again
-    stats = solver.solve()
-    assert_equals(stats["Lower bound"], 1030.0)
-
-    # New constraint should now be satisfied
-    assert solver.is_constraint_satisfied(cobj)
+    # Constraint should not be satisfied by current solution
+    assert not solver.is_constraint_satisfied(cut)
 
 
 def run_warm_start_tests(solver: InternalSolver) -> None:

tests/components/test_dynamic_user_cuts.py

@@ -12,6 +12,7 @@ from gurobipy import GRB
 from networkx import Graph
 from overrides import overrides
 
+from miplearn import InternalSolver
 from miplearn.components.dynamic_user_cuts import UserCutsComponent
 from miplearn.instance.base import Instance
 from miplearn.solvers.gurobi import GurobiSolver
@@ -49,10 +50,15 @@ class GurobiStableSetProblem(Instance):
         return violations
 
     @overrides
-    def build_user_cut(self, model: Any, cid: Hashable) -> Any:
+    def enforce_user_cut(
+        self,
+        solver: InternalSolver,
+        model: Any,
+        cid: Hashable,
+    ) -> Any:
         assert isinstance(cid, FrozenSet)
         x = model.getVars()
-        return gp.quicksum([x[i] for i in cid]) <= 1
+        model.addConstr(gp.quicksum([x[i] for i in cid]) <= 1)
 
 
 @pytest.fixture

tests/components/test_static_lazy.py

@@ -78,12 +78,14 @@ def features() -> Features:
 
 
 def test_usage_with_solver(instance: Instance) -> None:
+    assert instance.features is not None
+    assert instance.features.constraints is not None
+
     solver = Mock(spec=LearningSolver)
     solver.use_lazy_cb = False
     solver.gap_tolerance = 1e-4
 
     internal = solver.internal_solver = Mock(spec=InternalSolver)
-    internal.extract_constraint = Mock(side_effect=lambda cid: "<%s>" % cid)
     internal.is_constraint_satisfied = Mock(return_value=False)
 
     component = StaticLazyConstraintsComponent(violation_tolerance=1.0)
@@ -128,8 +130,8 @@ def test_usage_with_solver(instance: Instance) -> None:
     component.classifiers["type-b"].predict_proba.assert_called_once()
 
     # Should ask internal solver to remove some constraints
-    assert internal.extract_constraint.call_count == 1
-    internal.extract_constraint.assert_has_calls([call("c3")])
+    assert internal.remove_constraint.call_count == 1
+    internal.remove_constraint.assert_has_calls([call("c3")])
 
     # LearningSolver calls after_iteration (first time)
     should_repeat = component.iteration_cb(solver, instance, None)
@@ -137,9 +139,10 @@ def test_usage_with_solver(instance: Instance) -> None:
 
     # Should ask internal solver to verify if constraints in the pool are
     # satisfied and add the ones that are not
-    internal.is_constraint_satisfied.assert_called_once_with("<c3>", tol=1.0)
+    c3 = instance.features.constraints["c3"]
+    internal.is_constraint_satisfied.assert_called_once_with(c3, tol=1.0)
     internal.is_constraint_satisfied.reset_mock()
-    internal.add_constraint.assert_called_once_with("<c3>")
+    internal.add_constraint.assert_called_once_with(c3, name="c3")
     internal.add_constraint.reset_mock()
 
     # LearningSolver calls after_iteration (second time)