Document TorchAdapter._untransform_objective_thresholds, remove unused kwarg (facebook#3400)

Summary:

As titled. Just adding clarity to methods that make me question "what does this do, what is it used for?"

Differential Revision: D69989096

Author: saitcakmak

ax/modelbridge/torch.py

@@ -238,7 +238,6 @@ def infer_objective_thresholds(
         return self._untransform_objective_thresholds(
             objective_thresholds=obj_thresholds,
             objective_weights=torch_opt_config.objective_weights,
-            bounds=search_space_digest.bounds,
             opt_config_metrics=torch_opt_config.opt_config_metrics,
             fixed_features=torch_opt_config.fixed_features,
         )
@@ -727,7 +726,6 @@ def _gen(
                 self._untransform_objective_thresholds(
                     objective_thresholds=gen_metadata["objective_thresholds"],
                     objective_weights=torch_opt_config.objective_weights,
-                    bounds=search_space_digest.bounds,
                     opt_config_metrics=torch_opt_config.opt_config_metrics,
                     fixed_features=torch_opt_config.fixed_features,
                 )
@@ -923,24 +921,38 @@ def _untransform_objective_thresholds(
         self,
         objective_thresholds: Tensor,
         objective_weights: Tensor,
-        bounds: list[tuple[int | float, int | float]],
         opt_config_metrics: dict[str, Metric],
         fixed_features: dict[int, float] | None,
     ) -> list[ObjectiveThreshold]:
-        thresholds_np = objective_thresholds.cpu().numpy()
+        """Converts tensor-valued (possibly inferred) objective thresholds to
+        ``ObjectiveThreshold`` objects, and untransforms to ensure they are
+        on the same raw scale as the original optimization config.
+
+        Args:
+            objective_thresholds: A tensor of (possibly inferred) objective thresholds
+                of shape `(num_metrics)`.
+            objective_weights: A tensor of objective weights that denote whether each
+                objective is being minimized (-1) or maximized (+1). May also include
+                0 values, which represents outcome constraints and tracking metrics.
+            opt_config_metrics: A dictionary mapping the metric name to the ``Metric``
+                object from the original optimization config.
+            fixed_features: A map {feature_index: value} for features that should be
+                fixed to a particular value during generation. This typically includes
+                the target trial index for multi-task applications.
+
+        Returns:
+            A list of ``ObjectiveThreshold``s on the raw, untransformed scale.
+        """
         idxs = objective_weights.nonzero().view(-1).tolist()
 
-        # Create transformed ObjectiveThresholds from numpy thresholds.
+        # Create transformed ObjectiveThresholds from tensor thresholds.
         thresholds = []
         for idx in idxs:
             sign = torch.sign(objective_weights[idx])
             thresholds.append(
                 ObjectiveThreshold(
                     metric=opt_config_metrics[self.outcomes[idx]],
-                    # pyre-fixme[6]: In call `ObjectiveThreshold.__init__`,
-                    # for argument `bound`, expected `float` but got
-                    # `ndarray[typing.Any, typing.Any]`
-                    bound=thresholds_np[idx],
+                    bound=float(objective_thresholds[idx].item()),
                     relative=False,
                     op=ComparisonOp.LEQ if sign < 0 else ComparisonOp.GEQ,
                 )