Source code for ax.models.torch.botorch_modular.acquisition

#!/usr/bin/env python3
# Copyright (c) Meta Platforms, Inc. and affiliates.
#
# This source code is licensed under the MIT license found in the
# LICENSE file in the root directory of this source tree.

from __future__ import annotations

import dataclasses
import operator
import warnings
from functools import partial, reduce
from itertools import product
from typing import Any, Callable, Dict, List, Optional, Tuple, Type

import torch
from ax.core.search_space import SearchSpaceDigest
from ax.exceptions.core import AxWarning, SearchSpaceExhausted
from ax.models.model_utils import enumerate_discrete_combinations, mk_discrete_choices
from ax.models.torch.botorch_modular.optimizer_argparse import optimizer_argparse
from ax.models.torch.botorch_modular.surrogate import Surrogate
from ax.models.torch.botorch_moo_defaults import infer_objective_thresholds
from ax.models.torch.utils import (
    _get_X_pending_and_observed,
    get_botorch_objective_and_transform,
    subset_model,
)
from ax.models.torch_base import TorchOptConfig
from ax.utils.common.base import Base
from ax.utils.common.constants import Keys
from ax.utils.common.typeutils import not_none
from botorch.acquisition.acquisition import AcquisitionFunction
from botorch.acquisition.input_constructors import get_acqf_input_constructor
from botorch.acquisition.knowledge_gradient import qKnowledgeGradient
from botorch.acquisition.objective import MCAcquisitionObjective, PosteriorTransform
from botorch.acquisition.risk_measures import RiskMeasureMCObjective
from botorch.models.model import Model
from botorch.optim.optimize import (
    optimize_acqf,
    optimize_acqf_discrete,
    optimize_acqf_discrete_local_search,
    optimize_acqf_mixed,
)
from torch import Tensor


DUPLICATE_TOL = 1e-6
MAX_CHOICES_ENUMERATE = 100_000


[docs]class Acquisition(Base): """ **All classes in 'botorch_modular' directory are under construction, incomplete, and should be treated as alpha versions only.** Ax wrapper for BoTorch `AcquisitionFunction`, subcomponent of `BoTorchModel` and is not meant to be used outside of it. Args: surrogate: Surrogate model, with which this acquisition function will be used. search_space_digest: A SearchSpaceDigest object containing metadata about the search space (e.g. bounds, parameter types). torch_opt_config: A TorchOptConfig object containing optimization arguments (e.g., objective weights, constraints). botorch_acqf_class: Type of BoTorch `AcquistitionFunction` that should be used. Subclasses of `Acquisition` often specify these via `default_botorch_acqf_class` attribute, in which case specifying one here is not required. options: Optional mapping of kwargs to the underlying `Acquisition Function` in BoTorch. """ surrogate: Surrogate acqf: AcquisitionFunction def __init__( self, surrogate: Surrogate, search_space_digest: SearchSpaceDigest, torch_opt_config: TorchOptConfig, botorch_acqf_class: Type[AcquisitionFunction], options: Optional[Dict[str, Any]] = None, ) -> None: self.surrogate = surrogate # pyre-fixme[4]: Attribute must be annotated. self.options = options or {} X_pending, X_observed = _get_X_pending_and_observed( Xs=self.surrogate.Xs, objective_weights=torch_opt_config.objective_weights, bounds=search_space_digest.bounds, pending_observations=torch_opt_config.pending_observations, outcome_constraints=torch_opt_config.outcome_constraints, linear_constraints=torch_opt_config.linear_constraints, fixed_features=torch_opt_config.fixed_features, ) # Store objective thresholds for all outcomes (including non-objectives). self._objective_thresholds: Optional[ Tensor ] = torch_opt_config.objective_thresholds self._full_objective_weights: Tensor = torch_opt_config.objective_weights full_outcome_constraints = torch_opt_config.outcome_constraints # Subset model only to the outcomes we need for the optimization. if self.options.get(Keys.SUBSET_MODEL, True): subset_model_results = subset_model( model=self.surrogate.model, objective_weights=torch_opt_config.objective_weights, outcome_constraints=torch_opt_config.outcome_constraints, objective_thresholds=torch_opt_config.objective_thresholds, ) model = subset_model_results.model objective_weights = subset_model_results.objective_weights outcome_constraints = subset_model_results.outcome_constraints objective_thresholds = subset_model_results.objective_thresholds subset_idcs = subset_model_results.indices else: model = self.surrogate.model objective_weights = torch_opt_config.objective_weights outcome_constraints = torch_opt_config.outcome_constraints objective_thresholds = torch_opt_config.objective_thresholds subset_idcs = None # If objective weights suggest multiple objectives but objective # thresholds are not specified, infer them using the model that # has already been subset to avoid re-subsetting it within # `inter_objective_thresholds`. if ( objective_weights.nonzero().numel() > 1 and self._objective_thresholds is None ): if torch_opt_config.risk_measure is not None: # TODO[T131759263]: modify the heuristic to support risk measures. raise NotImplementedError( # pragma: no cover "Objective thresholds must be provided when using risk measures." ) self._objective_thresholds = infer_objective_thresholds( model=model, objective_weights=self._full_objective_weights, outcome_constraints=full_outcome_constraints, X_observed=X_observed, subset_idcs=subset_idcs, ) objective_thresholds = ( not_none(self._objective_thresholds)[subset_idcs] if subset_idcs is not None else self._objective_thresholds ) objective, posterior_transform = self.get_botorch_objective_and_transform( botorch_acqf_class=botorch_acqf_class, model=model, objective_weights=objective_weights, objective_thresholds=objective_thresholds, outcome_constraints=outcome_constraints, X_observed=X_observed, risk_measure=torch_opt_config.risk_measure, ) model_deps = self.compute_model_dependencies( surrogate=surrogate, search_space_digest=search_space_digest, torch_opt_config=dataclasses.replace( torch_opt_config, objective_weights=objective_weights, outcome_constraints=outcome_constraints, objective_thresholds=objective_thresholds, ), options=self.options, ) input_constructor_kwargs = { "X_baseline": X_observed, "X_pending": X_pending, "objective_thresholds": objective_thresholds, "outcome_constraints": outcome_constraints, "target_fidelities": search_space_digest.target_fidelities, "bounds": search_space_digest.bounds, **model_deps, **self.options, } input_constructor = get_acqf_input_constructor(botorch_acqf_class) # Handle multi-dataset surrogates - TODO: Improve this if len(self.surrogate.training_data) == 1: training_data = self.surrogate.training_data[0] else: training_data = dict( zip(not_none(self.surrogate._outcomes), self.surrogate.training_data) ) acqf_inputs = input_constructor( model=model, training_data=training_data, objective=objective, posterior_transform=posterior_transform, **input_constructor_kwargs, ) self.acqf = botorch_acqf_class(**acqf_inputs) # pyre-ignore [45] self.X_pending: Optional[Tensor] = X_pending self.X_observed: Tensor = not_none(X_observed) @property def botorch_acqf_class(self) -> Type[AcquisitionFunction]: """BoTorch ``AcquisitionFunction`` class underlying this ``Acquisition``.""" return self.acqf.__class__ @property def dtype(self) -> Optional[torch.dtype]: """Torch data type of the tensors in the training data used in the model, of which this ``Acquisition`` is a subcomponent. """ return self.surrogate.dtype @property def device(self) -> Optional[torch.device]: """Torch device type of the tensors in the training data used in the model, of which this ``Acquisition`` is a subcomponent. """ return self.surrogate.device @property def objective_thresholds(self) -> Optional[Tensor]: """The objective thresholds for all outcomes. For non-objective outcomes, the objective thresholds are nans. """ return self._objective_thresholds @property def objective_weights(self) -> Optional[Tensor]: """The objective weights for all outcomes.""" return self._full_objective_weights
[docs] def optimize( self, n: int, search_space_digest: SearchSpaceDigest, inequality_constraints: Optional[List[Tuple[Tensor, Tensor, float]]] = None, fixed_features: Optional[Dict[int, float]] = None, rounding_func: Optional[Callable[[Tensor], Tensor]] = None, optimizer_options: Optional[Dict[str, Any]] = None, ) -> Tuple[Tensor, Tensor]: """Generate a set of candidates via multi-start optimization. Obtains candidates and their associated acquisition function values. Args: n: The number of candidates to generate. search_space_digest: A ``SearchSpaceDigest`` object containing search space properties, e.g. ``bounds`` for optimization. inequality_constraints: A list of tuples (indices, coefficients, rhs), with each tuple encoding an inequality constraint of the form ``sum_i (X[indices[i]] * coefficients[i]) >= rhs``. fixed_features: A map `{feature_index: value}` for features that should be fixed to a particular value during generation. rounding_func: A function that post-processes an optimization result appropriately (i.e., according to `round-trip` transformations). optimizer_options: Options for the optimizer function, e.g. ``sequential`` or ``raw_samples``. """ # NOTE: Could make use of `optimizer_class` when it's added to BoTorch # instead of calling `optimizer_acqf` or `optimize_acqf_discrete` etc. _tensorize = partial(torch.tensor, dtype=self.dtype, device=self.device) ssd = search_space_digest bounds = _tensorize(ssd.bounds).t() # Prepare arguments for optimizer optimizer_options_with_defaults = optimizer_argparse( self.acqf, bounds=bounds, q=n, optimizer_options=optimizer_options, ) discrete_features = sorted(ssd.ordinal_features + ssd.categorical_features) if fixed_features is not None: for i in fixed_features: if not 0 <= i < len(ssd.feature_names): raise ValueError(f"Invalid fixed_feature index: {i}") # 1. Handle the fully continuous search space. if not discrete_features: return optimize_acqf( acq_function=self.acqf, bounds=bounds, q=n, inequality_constraints=inequality_constraints, fixed_features=fixed_features, post_processing_func=rounding_func, **optimizer_options_with_defaults, ) # 2. Handle search spaces with discrete features. discrete_choices = mk_discrete_choices(ssd=ssd, fixed_features=fixed_features) # 2a. Handle the fully discrete search space. if len(discrete_choices) == len(ssd.feature_names): X_observed = self.X_observed if self.X_pending is not None: X_observed = torch.cat([X_observed, self.X_pending], dim=0) # Special handling for search spaces with a large number of choices total_choices = reduce( operator.mul, [float(len(c)) for c in discrete_choices.values()] ) if total_choices > MAX_CHOICES_ENUMERATE: discrete_choices = [ torch.tensor(c, device=self.device, dtype=self.dtype) for c in discrete_choices.values() ] return optimize_acqf_discrete_local_search( acq_function=self.acqf, q=n, discrete_choices=discrete_choices, inequality_constraints=inequality_constraints, X_avoid=X_observed, **optimizer_options_with_defaults, ) # Enumerate all possible choices all_choices = (discrete_choices[i] for i in range(len(discrete_choices))) all_choices = _tensorize(tuple(product(*all_choices))) # This can be vectorized, but using a for-loop to avoid memory issues for x in X_observed: all_choices = all_choices[ (all_choices - x).abs().max(dim=-1).values > DUPLICATE_TOL ] # Filter out candidates that violate the constraints # TODO: It will be more memory-efficient to do this filtering before # converting the generator into a tensor. However, if we run into memory # issues we are likely better off being smarter in how we optimize the # acquisition function. inequality_constraints = inequality_constraints or [] is_feasible = torch.ones(all_choices.shape[0], dtype=torch.bool) for (inds, weights, bound) in inequality_constraints: is_feasible &= (all_choices[..., inds] * weights).sum(dim=-1) >= bound all_choices = all_choices[is_feasible] num_choices = all_choices.size(dim=0) if num_choices == 0: raise SearchSpaceExhausted( "No more feasible choices in a fully discrete search space." ) if num_choices < n: warnings.warn( ( f"Requested n={n} candidates from fully discrete search " f"space, but only {num_choices} possible choices remain." ), AxWarning, ) n = num_choices return optimize_acqf_discrete( acq_function=self.acqf, q=n, choices=all_choices, **optimizer_options_with_defaults, ) # 2b. Handle mixed search spaces that have discrete and continuous features. return optimize_acqf_mixed( acq_function=self.acqf, bounds=bounds, q=n, # For now we just enumerate all possible discrete combinations. This is not # scalable and and only works for a reasonably small number of choices. A # slowdown warning is logged in `enumerate_discrete_combinations` if needed. fixed_features_list=enumerate_discrete_combinations( discrete_choices=discrete_choices ), inequality_constraints=inequality_constraints, post_processing_func=rounding_func, **optimizer_options_with_defaults, )
[docs] def evaluate(self, X: Tensor) -> Tensor: """Evaluate the acquisition function on the candidate set `X`. Args: X: A `batch_shape x q x d`-dim Tensor of t-batches with `q` `d`-dim design points each. Returns: A `batch_shape'`-dim Tensor of acquisition values at the given design points `X`, where `batch_shape'` is the broadcasted batch shape of model and input `X`. """ if isinstance(self.acqf, qKnowledgeGradient): return self.acqf.evaluate(X=X) else: # NOTE: `AcquisitionFunction.__call__` calls `forward`, # so below is equivalent to `self.acqf.forward(X=X)`. return self.acqf(X=X)
[docs] def compute_model_dependencies( self, surrogate: Surrogate, search_space_digest: SearchSpaceDigest, torch_opt_config: TorchOptConfig, options: Optional[Dict[str, Any]] = None, ) -> Dict[str, Any]: """Computes inputs to acquisition function class based on the given surrogate model. NOTE: When subclassing `Acquisition` from a superclass where this method returns a non-empty dictionary of kwargs to `AcquisitionFunction`, call `super().compute_model_dependencies` and then update that dictionary of options with the options for the subclass you are creating (unless the superclass' model dependencies should not be propagated to the subclass). See `MultiFidelityKnowledgeGradient.compute_model_dependencies` for an example. Args: surrogate: The surrogate object containing the BoTorch `Model`, with which this `Acquisition` is to be used. search_space_digest: A SearchSpaceDigest object containing metadata about the search space (e.g. bounds, parameter types). torch_opt_config: A TorchOptConfig object containing optimization arguments (e.g., objective weights, constraints). options: The `options` kwarg dict, passed on initialization of the `Acquisition` object. Returns: A dictionary of surrogate model-dependent options, to be passed as kwargs to BoTorch`AcquisitionFunction` constructor. """ return {}
[docs] def get_botorch_objective_and_transform( self, botorch_acqf_class: Type[AcquisitionFunction], model: Model, objective_weights: Tensor, objective_thresholds: Optional[Tensor] = None, outcome_constraints: Optional[Tuple[Tensor, Tensor]] = None, X_observed: Optional[Tensor] = None, risk_measure: Optional[RiskMeasureMCObjective] = None, ) -> Tuple[Optional[MCAcquisitionObjective], Optional[PosteriorTransform]]: return get_botorch_objective_and_transform( model=model, objective_weights=objective_weights, outcome_constraints=outcome_constraints, objective_thresholds=objective_thresholds, X_observed=X_observed, risk_measure=risk_measure, )