From 4057a6550608e2db0753f69d0ebd7089bb8927b6 Mon Sep 17 00:00:00 2001
From: "Alinson S. Xavier" <git@axavier.org>
Date: Thu, 7 Jan 2021 11:54:00 -0600
Subject: [PATCH] ConvertTightIneqs: Convert only inequalities, not equalities

---
 miplearn/components/steps/convert_tight.py   | 2 +-
 miplearn/components/steps/drop_redundant.py  | 2 +-
 miplearn/components/tests/test_relaxation.py | 6 +++---
 miplearn/solvers/gurobi.py                   | 5 +++--
 miplearn/solvers/internal.py                 | 2 +-
 miplearn/solvers/pyomo/base.py               | 2 +-
 6 files changed, 10 insertions(+), 9 deletions(-)

diff --git a/miplearn/components/steps/convert_tight.py b/miplearn/components/steps/convert_tight.py
index 4b7fb96..bfd1bf6 100644
--- a/miplearn/components/steps/convert_tight.py
+++ b/miplearn/components/steps/convert_tight.py
@@ -57,7 +57,7 @@ class ConvertTightIneqsIntoEqsStep(Component):
         logger.info(f"Converted {n_converted} inequalities into equalities")
 
     def after_solve(self, solver, instance, model, results):
-        instance.slacks = solver.internal_solver.get_constraint_slacks()
+        instance.slacks = solver.internal_solver.get_inequality_slacks()
 
     def fit(self, training_instances):
         logger.debug("Extracting x and y...")
diff --git a/miplearn/components/steps/drop_redundant.py b/miplearn/components/steps/drop_redundant.py
index 7682bd2..f642bfa 100644
--- a/miplearn/components/steps/drop_redundant.py
+++ b/miplearn/components/steps/drop_redundant.py
@@ -68,7 +68,7 @@ class DropRedundantInequalitiesStep(Component):
         logger.info("Extracted %d predicted constraints" % len(self.pool))
 
     def after_solve(self, solver, instance, model, results):
-        instance.slacks = solver.internal_solver.get_constraint_slacks()
+        instance.slacks = solver.internal_solver.get_inequality_slacks()
 
     def fit(self, training_instances):
         logger.debug("Extracting x and y...")
diff --git a/miplearn/components/tests/test_relaxation.py b/miplearn/components/tests/test_relaxation.py
index e901543..c172c7a 100644
--- a/miplearn/components/tests/test_relaxation.py
+++ b/miplearn/components/tests/test_relaxation.py
@@ -14,7 +14,7 @@ def _setup():
 
     internal = solver.internal_solver = Mock(spec=InternalSolver)
     internal.get_constraint_ids = Mock(return_value=["c1", "c2", "c3", "c4"])
-    internal.get_constraint_slacks = Mock(
+    internal.get_inequality_slacks = Mock(
         side_effect=lambda: {
             "c1": 0.5,
             "c2": 0.0,
@@ -112,8 +112,8 @@ def test_drop_redundant():
     # LearningSolver calls after_solve
     component.after_solve(solver, instance, None, None)
 
-    # Should query slack for all constraints
-    internal.get_constraint_slacks.assert_called_once()
+    # Should query slack for all inequalities
+    internal.get_inequality_slacks.assert_called_once()
 
     # Should store constraint slacks in instance object
     assert hasattr(instance, "slacks")
diff --git a/miplearn/solvers/gurobi.py b/miplearn/solvers/gurobi.py
index e76f738..f469c65 100644
--- a/miplearn/solvers/gurobi.py
+++ b/miplearn/solvers/gurobi.py
@@ -271,8 +271,9 @@ class GurobiSolver(InternalSolver):
         else:
             raise Exception("Unknown sense: %s" % sense)
 
-    def get_constraint_slacks(self):
-        return {c.ConstrName: c.Slack for c in self.model.getConstrs()}
+    def get_inequality_slacks(self):
+        ineqs = [c for c in self.model.getConstrs() if c.sense != "="]
+        return {c.ConstrName: c.Slack for c in ineqs}
 
     def set_constraint_sense(self, cid, sense):
         c = self.model.getConstrByName(cid)
diff --git a/miplearn/solvers/internal.py b/miplearn/solvers/internal.py
index 84c946b..334175a 100644
--- a/miplearn/solvers/internal.py
+++ b/miplearn/solvers/internal.py
@@ -184,7 +184,7 @@ class InternalSolver(ABC):
         pass
 
     @abstractmethod
-    def get_constraint_slacks(self):
+    def get_inequality_slacks(self):
         """
         Returns a dictionary mapping constraint name to the constraint slack
         in the current solution.
diff --git a/miplearn/solvers/pyomo/base.py b/miplearn/solvers/pyomo/base.py
index d44de7e..eca4903 100644
--- a/miplearn/solvers/pyomo/base.py
+++ b/miplearn/solvers/pyomo/base.py
@@ -252,7 +252,7 @@ class BasePyomoSolver(InternalSolver):
     def relax(self):
         raise Exception("not implemented")
 
-    def get_constraint_slacks(self):
+    def get_inequality_slacks(self):
         raise Exception("not implemented")
 
     def set_constraint_sense(self, cid, sense):