Fix input constructor for qMultiFidelityKnowledgeGradient

Summary:
The input constructor for `qMultiFidelityKnowledgeGradient` was computing `current_value` in a manner that was effectively not fidelity-aware (the fidelity dimension was not fixed in the optimization done to obtain `current_value`), since it was simply re-using functionality from the input constructor for `construct_inputs_qKG`.

This diff addresses this by making use of `target_fidelities` as the `fixed_features` argument to `D62380369`.

Differential Revision: D62391106

botorch/acquisition/input_constructors.py

@@ -1255,26 +1255,38 @@ def construct_inputs_qMFKG(
     cost_intercept: float = 1.0,
     num_trace_observations: int = 0,
     num_fantasies: int = 64,
+    **optimize_objective_kwargs: TOptimizeObjectiveKwargs,
 ) -> dict[str, Any]:
     r"""Construct kwargs for `qMultiFidelityKnowledgeGradient` constructor."""
 
+    X = _get_dataset_field(training_data, "X", first_only=True)
+    _bounds = torch.as_tensor(bounds, dtype=X.dtype, device=X.device)
+
     inputs_mf = construct_inputs_mf_base(
         target_fidelities=target_fidelities,
         fidelity_weights=fidelity_weights,
         cost_intercept=cost_intercept,
         num_trace_observations=num_trace_observations,
     )
 
-    inputs_kg = construct_inputs_qKG(
+    _, current_value = optimize_objective(
         model=model,
-        training_data=training_data,
-        bounds=bounds,
+        bounds=_bounds.t(),
+        q=1,
         objective=objective,
         posterior_transform=posterior_transform,
-        num_fantasies=num_fantasies,
+        fixed_features=target_fidelities,
+        **optimize_objective_kwargs,
     )
 
-    return {**inputs_mf, **inputs_kg}
+    return {
+        "model": model,
+        "objective": objective,
+        "posterior_transform": posterior_transform,
+        "num_fantasies": num_fantasies,
+        "current_value": current_value.detach().cpu().max(),
+        **inputs_mf,
+    }
 
 
 @acqf_input_constructor(qMultiFidelityMaxValueEntropy)

test/acquisition/test_input_constructors.py

@@ -1304,28 +1304,49 @@ def test_construct_inputs_mf_base(self) -> None:
                 )
 
     def test_construct_inputs_mfkg(self) -> None:
+        current_value = torch.tensor(1.23)
+
         constructor_args = {
-            "model": None,
+            "model": self.mock_model,
             "training_data": self.blockX_blockY,
-            "objective": None,
             "bounds": self.bounds,
-            "num_fantasies": 123,
             "target_fidelities": {0: 0.987},
+            "objective": None,
             "fidelity_weights": {0: 0.654},
             "cost_intercept": 0.321,
+            "num_fantasies": 123,
         }
 
         input_constructor = get_acqf_input_constructor(qMultiFidelityKnowledgeGradient)
         with mock.patch(
-            target="botorch.acquisition.input_constructors.construct_inputs_mf_base",
-            return_value={"foo": 0},
-        ), mock.patch(
-            target="botorch.acquisition.input_constructors.construct_inputs_qKG",
-            return_value={"bar": 1},
-        ):
+            target="botorch.acquisition.input_constructors.optimize_acqf",
+            return_value=(None, current_value),
+        ) as mock_optimize_acqf:
             inputs_mfkg = input_constructor(**constructor_args)
-        inputs_test = {"foo": 0, "bar": 1}
-        self.assertEqual(inputs_mfkg, inputs_test)
+
+            mock_optimize_acqf_kwargs = mock_optimize_acqf.call_args[1]
+
+            self.assertIsInstance(
+                mock_optimize_acqf_kwargs["acq_function"],
+                FixedFeatureAcquisitionFunction,
+            )
+            self.assertLessEqual(
+                {
+                    "model",
+                    "objective",
+                    "current_value",
+                    "project",
+                    "expand",
+                    "cost_aware_utility",
+                    "posterior_transform",
+                    "num_fantasies",
+                },
+                set(inputs_mfkg.keys()),
+            )
+            self.assertEqual(
+                inputs_mfkg["num_fantasies"], constructor_args["num_fantasies"]
+            )
+            self.assertEqual(inputs_mfkg["current_value"], current_value)
 
     def test_construct_inputs_mfmes(self) -> None:
         target_fidelities = {0: 0.987}
@@ -1467,6 +1488,18 @@ def setUp(self, suppress_input_warnings: bool = True) -> None:
             },
         )
         self.cases["MF look-ahead"] = (
+            [qMultiFidelityMaxValueEntropy],
+            {
+                "model": kg_model,
+                "training_data": self.blockX_blockY,
+                "bounds": bounds,
+                "target_fidelities": {0: 0.987},
+                "num_fantasies": 30,
+            },
+        )
+        bounds = torch.ones((2, 2))
+        kg_model = SingleTaskGP(train_X=torch.rand((3, 2)), train_Y=torch.rand((3, 1)))
+        self.cases["MF look-ahead (KG)"] = (
             [qMultiFidelityKnowledgeGradient, qMultiFidelityMaxValueEntropy],
             {
                 "model": kg_model,