Support per-metric model specification in MBM

ax/modelbridge/tests/test_registry.py

@@ -10,6 +10,7 @@
 
 import torch
 from ax.core.observation import ObservationFeatures
+from ax.core.optimization_config import MultiObjectiveOptimizationConfig
 from ax.modelbridge.discrete import DiscreteModelBridge
 from ax.modelbridge.random import RandomModelBridge
 from ax.modelbridge.registry import (
@@ -99,7 +100,8 @@ def test_SAASBO(self) -> None:
             SurrogateSpec(botorch_model_class=SaasFullyBayesianSingleTaskGP),
         )
         self.assertEqual(
-            saasbo.model.surrogate.botorch_model_class, SaasFullyBayesianSingleTaskGP
+            saasbo.model.surrogate.model_configs[0].botorch_model_class,
+            SaasFullyBayesianSingleTaskGP,
         )
 
     @mock_botorch_optimize
@@ -459,9 +461,16 @@ def test_ST_MTGP(self, use_saas: bool = False) -> None:
                 self.assertIsInstance(mtgp, TorchModelBridge)
                 self.assertIsInstance(mtgp.model, BoTorchModel)
                 self.assertEqual(mtgp.model.acquisition_class, Acquisition)
-                self.assertIsInstance(mtgp.model.surrogate.model, ModelListGP)
+                is_moo = isinstance(
+                    exp.optimization_config, MultiObjectiveOptimizationConfig
+                )
+                if is_moo:
+                    self.assertIsInstance(mtgp.model.surrogate.model, ModelListGP)
+                    models = mtgp.model.surrogate.model.models
+                else:
+                    models = [mtgp.model.surrogate.model]
 
-                for model in mtgp.model.surrogate.model.models:
+                for model in models:
                     self.assertIsInstance(
                         model,
                         SaasFullyBayesianMultiTaskGP if use_saas else MultiTaskGP,

ax/models/torch/botorch_modular/model.py

@@ -28,6 +28,7 @@
     check_outcome_dataset_match,
     choose_botorch_acqf_class,
     construct_acquisition_and_optimizer_options,
+    ModelConfig,
 )
 from ax.models.torch.utils import _to_inequality_constraints
 from ax.models.torch_base import TorchGenResults, TorchModel, TorchOptConfig
@@ -79,6 +80,8 @@ class SurrogateSpec:
 
     allow_batched_models: bool = True
 
+    model_configs: list[ModelConfig] = field(default_factory=list)
+    metric_to_model_configs: dict[str, list[ModelConfig]] = field(default_factory=dict)
     outcomes: list[str] = field(default_factory=list)
 
 
@@ -241,13 +244,19 @@ def fit(
                     input_transform_options=spec.input_transform_options,
                     outcome_transform_classes=spec.outcome_transform_classes,
                     outcome_transform_options=spec.outcome_transform_options,
+                    model_configs=spec.model_configs,
+                    metric_to_model_configs=spec.metric_to_model_configs,
                     allow_batched_models=spec.allow_batched_models,
                 )
             else:
                 self._surrogate = Surrogate()
 
         # Fit the surrogate.
-        self.surrogate.model_options.update(additional_model_inputs)
+        for config in self.surrogate.model_configs:
+            config.model_options.update(additional_model_inputs)
+        for config_list in self.surrogate.metric_to_model_configs.values():
+            for config in config_list:
+                config.model_options.update(additional_model_inputs)
         self.surrogate.fit(
             datasets=datasets,
             search_space_digest=search_space_digest,

ax/models/torch/botorch_modular/utils.py

@@ -9,6 +9,7 @@
 import warnings
 from collections import OrderedDict
 from collections.abc import Sequence
+from dataclasses import dataclass, field
 from logging import Logger
 from typing import Any
 
@@ -34,29 +35,138 @@
 from botorch.models.model import Model, ModelList
 from botorch.models.multitask import MultiTaskGP
 from botorch.models.pairwise_gp import PairwiseGP
+from botorch.models.transforms.input import InputTransform
+from botorch.models.transforms.outcome import OutcomeTransform
 from botorch.utils.datasets import SupervisedDataset
 from botorch.utils.transforms import is_fully_bayesian
+from gpytorch.kernels.kernel import Kernel
+from gpytorch.likelihoods import Likelihood
+from gpytorch.mlls.exact_marginal_log_likelihood import ExactMarginalLogLikelihood
 from gpytorch.mlls.marginal_log_likelihood import MarginalLogLikelihood
 from torch import Tensor
 
 MIN_OBSERVED_NOISE_LEVEL = 1e-7
 logger: Logger = get_logger(__name__)
 
 
+@dataclass
+class ModelConfig:
+    """Configuration for the BoTorch Model used in Surrogate.
+
+    Args:
+        botorch_model_class: ``Model`` class to be used as the underlying
+            BoTorch model. If None is provided a model class will be selected (either
+            one for all outcomes or a ModelList with separate models for each outcome)
+            will be selected automatically based off the datasets at `construct` time.
+            This argument is deprecated in favor of model_configs.
+        model_options: Dictionary of options / kwargs for the BoTorch
+            ``Model`` constructed during ``Surrogate.fit``.
+            Note that the corresponding attribute will later be updated to include any
+            additional kwargs passed into ``BoTorchModel.fit``.
+            This argument is deprecated in favor of model_configs.
+        mll_class: ``MarginalLogLikelihood`` class to use for model-fitting.
+            This argument is deprecated in favor of model_configs.
+        mll_options: Dictionary of options / kwargs for the MLL. This argument is
+            deprecated in favor of model_configs.
+        outcome_transform_classes: List of BoTorch outcome transforms classes. Passed
+            down to the BoTorch ``Model``. Multiple outcome transforms can be chained
+            together using ``ChainedOutcomeTransform``. This argument is deprecated in
+            favor of model_configs.
+        outcome_transform_options: Outcome transform classes kwargs. The keys are
+            class string names and the values are dictionaries of outcome transform
+            kwargs. For example,
+            `
+            outcome_transform_classes = [Standardize]
+            outcome_transform_options = {
+                "Standardize": {"m": 1},
+            `
+            For more options see `botorch/models/transforms/outcome.py`. This argument
+                is deprecated in favor of model_configs.
+        input_transform_classes: List of BoTorch input transforms classes.
+            Passed down to the BoTorch ``Model``. Multiple input transforms
+            will be chained together using ``ChainedInputTransform``.
+            This argument is deprecated in favor of model_configs.
+        input_transform_options: Input transform classes kwargs. The keys are
+            class string names and the values are dictionaries of input transform
+            kwargs. For example,
+            `
+            input_transform_classes = [Normalize, Round]
+            input_transform_options = {
+                "Normalize": {"d": 3},
+                "Round": {"integer_indices": [0], "categorical_features": {1: 2}},
+            }
+            `
+            For more input options see `botorch/models/transforms/input.py`.
+            This argument is deprecated in favor of model_configs.
+        covar_module_class: Covariance module class. This gets initialized after
+            parsing the ``covar_module_options`` in ``covar_module_argparse``,
+            and gets passed to the model constructor as ``covar_module``.
+            This argument is deprecated in favor of model_configs.
+        covar_module_options: Covariance module kwargs. This argument is deprecated
+            in favor of model_configs.
+        likelihood: ``Likelihood`` class. This gets initialized with
+            ``likelihood_options`` and gets passed to the model constructor.
+            This argument is deprecated in favor of model_configs.
+        likelihood_options: Likelihood options. This argument is deprecated in favor
+            of model_configs.
+    """
+
+    botorch_model_class: type[Model] | None = None
+    model_options: dict[str, Any] = field(default_factory=dict)
+    mll_class: type[MarginalLogLikelihood] = ExactMarginalLogLikelihood
+    mll_options: dict[str, Any] = field(default_factory=dict)
+    input_transform_classes: list[type[InputTransform]] | None = None
+    input_transform_options: dict[str, dict[str, Any]] | None = field(
+        default_factory=dict
+    )
+    outcome_transform_classes: list[type[OutcomeTransform]] | None = None
+    outcome_transform_options: dict[str, dict[str, Any]] = field(default_factory=dict)
+    covar_module_class: type[Kernel] | None = None
+    covar_module_options: dict[str, Any] = field(default_factory=dict)
+    likelihood_class: type[Likelihood] | None = None
+    likelihood_options: dict[str, Any] = field(default_factory=dict)
+
+
 def use_model_list(
     datasets: Sequence[SupervisedDataset],
     botorch_model_class: type[Model],
+    model_configs: list[ModelConfig] | None = None,
+    metric_to_model_configs: dict[str, list[ModelConfig]] | None = None,
     allow_batched_models: bool = True,
 ) -> bool:
-    if issubclass(botorch_model_class, MultiTaskGP):
-        # We currently always wrap multi-task models into `ModelListGP`.
+    model_configs = model_configs or []
+    metric_to_model_configs = metric_to_model_configs or {}
+    if len(datasets) == 1 and datasets[0].Y.shape[-1] == 1:
+        # There is only one outcome, so we can use a single model.
+        return False
+    elif (
+        len(model_configs) > 1
+        or len(metric_to_model_configs) > 0
+        or any(len(model_config) for model_config in metric_to_model_configs.values())
+    ):
+        # There are multiple outcomes and outcomes might be modeled with different
+        # models
         return True
-    elif issubclass(botorch_model_class, SaasFullyBayesianSingleTaskGP):
+    # Otherwise, the same model class is used for all outcomes.
+    # Determine what the model class is.
+    if len(model_configs) > 0:
+        botorch_model_class = (
+            model_configs[0].botorch_model_class or botorch_model_class
+        )
+    if issubclass(botorch_model_class, SaasFullyBayesianSingleTaskGP):
         # SAAS models do not support multiple outcomes.
         # Use model list if there are multiple outcomes.
         return len(datasets) > 1 or datasets[0].Y.shape[-1] > 1
+    elif issubclass(botorch_model_class, MultiTaskGP):
+        # We wrap multi-task models into `ModelListGP` when there are
+        # multiple outcomes.
+        return len(datasets) > 1 or datasets[0].Y.shape[-1] > 1
     elif len(datasets) == 1:
-        # Just one outcome, can use single model.
+        # This method is called before multiple datasets are merged into
+        # one if using a batched model. If there is one dataset here,
+        # there should be a reason that a single model should be used:
+        # e.g. a contextual model, where we want to jointly model the metric
+        # each context (and context-level metrics are different outcomes).
         return False
     elif issubclass(botorch_model_class, BatchedMultiOutputGPyTorchModel) and all(
         torch.equal(datasets[0].X, ds.X) for ds in datasets[1:]

ax/models/torch/tests/test_model.py

@@ -27,6 +27,7 @@
 from ax.models.torch.botorch_modular.utils import (
     choose_model_class,
     construct_acquisition_and_optimizer_options,
+    ModelConfig,
 )
 from ax.models.torch.utils import _filter_X_observed
 from ax.models.torch_base import TorchOptConfig
@@ -327,7 +328,21 @@ def test_fit(self, mock_fit: Mock) -> None:
         mock_fit.assert_called_with(
             dataset=self.block_design_training_data[0],
             search_space_digest=self.mf_search_space_digest,
-            botorch_model_class=SingleTaskMultiFidelityGP,
+            model_config=ModelConfig(
+                botorch_model_class=None,
+                model_options={},
+                mll_class=ExactMarginalLogLikelihood,
+                mll_options={},
+                input_transform_classes=None,
+                input_transform_options={},
+                outcome_transform_classes=None,
+                outcome_transform_options={},
+                covar_module_class=None,
+                covar_module_options={},
+                likelihood_class=None,
+                likelihood_options={},
+            ),
+            default_botorch_model_class=SingleTaskMultiFidelityGP,
             state_dict=None,
             refit=True,
         )
@@ -727,6 +742,8 @@ def test_surrogate_model_options_propagation(
             input_transform_options=None,
             outcome_transform_classes=None,
             outcome_transform_options=None,
+            model_configs=[],
+            metric_to_model_configs={},
             allow_batched_models=True,
         )
 
@@ -755,6 +772,8 @@ def test_surrogate_options_propagation(
             input_transform_options=None,
             outcome_transform_classes=None,
             outcome_transform_options=None,
+            model_configs=[],
+            metric_to_model_configs={},
             allow_batched_models=False,
         )