Source code for botorch.sampling.normal
#!/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.
r"""
Sampler modules producing N(0,1) samples, to be used with MC-evaluated
acquisition functions and Gaussian posteriors.
"""
from __future__ import annotations
from abc import ABC, abstractmethod
import torch
from botorch.exceptions import UnsupportedError
from botorch.posteriors import Posterior
from botorch.posteriors.higher_order import HigherOrderGPPosterior
from botorch.posteriors.multitask import MultitaskGPPosterior
from botorch.posteriors.transformed import TransformedPosterior
from botorch.sampling.base import MCSampler
from botorch.utils.sampling import draw_sobol_normal_samples, manual_seed
from torch import Tensor
from torch.quasirandom import SobolEngine
[docs]
class NormalMCSampler(MCSampler, ABC):
r"""Base class for samplers producing (possibly QMC) N(0,1) samples.
Subclasses must implement the `_construct_base_samples` method.
"""
[docs]
def forward(self, posterior: Posterior) -> Tensor:
r"""Draws MC samples from the posterior.
Args:
posterior: The posterior to sample from.
Returns:
The samples drawn from the posterior.
"""
self._construct_base_samples(posterior=posterior)
samples = posterior.rsample_from_base_samples(
sample_shape=self.sample_shape,
base_samples=self.base_samples.expand(
self._get_extended_base_sample_shape(posterior=posterior)
),
)
return samples
@abstractmethod
def _construct_base_samples(self, posterior: Posterior) -> None:
r"""Generate base samples (if necessary).
This function will generate a new set of base samples and register the
`base_samples` buffer if one of the following is true:
- the MCSampler has no `base_samples` attribute.
- the output of `_get_collapsed_shape` does not agree with the shape of
`self.base_samples`.
Args:
posterior: The Posterior for which to generate base samples.
"""
pass # pragma: no cover
def _update_base_samples(
self, posterior: Posterior, base_sampler: MCSampler
) -> None:
r"""Update the sampler to use the original base samples for X_baseline.
This is used in CachedCholeskyAcquisitionFunctions to ensure consistency.
Args:
posterior: The posterior for which the base samples are constructed.
base_sampler: The base sampler to retrieve the base samples from.
"""
self._instance_check(base_sampler=base_sampler)
self._construct_base_samples(posterior=posterior)
if base_sampler.base_samples is not None:
current_base_samples = base_sampler.base_samples.detach().clone()
# This is the # of non-`sample_shape` dimensions.
base_ndims = current_base_samples.dim() - 1
# Unsqueeze as many dimensions as needed to match target_shape.
target_shape = self._get_collapsed_shape(posterior=posterior)
view_shape = (
self.sample_shape
+ torch.Size([1] * (len(target_shape) - current_base_samples.dim()))
+ current_base_samples.shape[-base_ndims:]
)
expanded_shape = (
target_shape[:-base_ndims] + current_base_samples.shape[-base_ndims:]
)
# Use stored base samples:
# Use all base_samples from the current sampler
# this includes the base_samples from the base_sampler
# and any base_samples for the new points in the sampler.
# For example, when using sequential greedy candidate generation
# then generate the new candidate point using last (-1) base_sample
# in sampler. This copies that base sample.
expanded_samples = current_base_samples.view(view_shape).expand(
expanded_shape
)
non_transformed_posterior = (
posterior._posterior
if isinstance(posterior, TransformedPosterior)
else posterior
)
if isinstance(
non_transformed_posterior,
(HigherOrderGPPosterior, MultitaskGPPosterior),
):
n_train_samples = current_base_samples.shape[-1] // 2
# The train base samples.
self.base_samples[..., :n_train_samples] = expanded_samples[
..., :n_train_samples
]
# The train noise base samples.
self.base_samples[..., -n_train_samples:] = expanded_samples[
..., -n_train_samples:
]
else:
batch_shape = non_transformed_posterior.batch_shape
single_output = (
len(posterior.base_sample_shape) - len(batch_shape)
) == 1
if single_output:
self.base_samples[..., : current_base_samples.shape[-1]] = (
expanded_samples
)
else:
self.base_samples[..., : current_base_samples.shape[-2], :] = (
expanded_samples
)
[docs]
class IIDNormalSampler(NormalMCSampler):
r"""Sampler for MC base samples using iid N(0,1) samples.
Example:
>>> sampler = IIDNormalSampler(1000, seed=1234)
>>> posterior = model.posterior(test_X)
>>> samples = sampler(posterior)
"""
def _construct_base_samples(self, posterior: Posterior) -> None:
r"""Generate iid `N(0,1)` base samples (if necessary).
This function will generate a new set of base samples and set the
`base_samples` buffer if one of the following is true:
- the MCSampler has no `base_samples` attribute.
- the output of `_get_collapsed_shape` does not agree with the shape of
`self.base_samples`.
Args:
posterior: The Posterior for which to generate base samples.
"""
target_shape = self._get_collapsed_shape(posterior=posterior)
if self.base_samples is None or self.base_samples.shape != target_shape:
with manual_seed(seed=self.seed):
base_samples = torch.randn(
target_shape, device=posterior.device, dtype=posterior.dtype
)
self.register_buffer("base_samples", base_samples)
if self.base_samples.device != posterior.device:
self.to(device=posterior.device) # pragma: nocover
if self.base_samples.dtype != posterior.dtype:
self.to(dtype=posterior.dtype)
[docs]
class SobolQMCNormalSampler(NormalMCSampler):
r"""Sampler for quasi-MC N(0,1) base samples using Sobol sequences.
Example:
>>> sampler = SobolQMCNormalSampler(torch.Size([1024]), seed=1234)
>>> posterior = model.posterior(test_X)
>>> samples = sampler(posterior)
"""
def _construct_base_samples(self, posterior: Posterior) -> None:
r"""Generate quasi-random Normal base samples (if necessary).
This function will generate a new set of base samples and set the
`base_samples` buffer if one of the following is true:
- the MCSampler has no `base_samples` attribute.
- the output of `_get_collapsed_shape` does not agree with the shape of
`self.base_samples`.
Args:
posterior: The Posterior for which to generate base samples.
"""
target_shape = self._get_collapsed_shape(posterior=posterior)
if self.base_samples is None or self.base_samples.shape != target_shape:
base_collapsed_shape = target_shape[len(self.sample_shape) :]
output_dim = base_collapsed_shape.numel()
if output_dim > SobolEngine.MAXDIM:
raise UnsupportedError(
"SobolQMCSampler only supports dimensions "
f"`q * o <= {SobolEngine.MAXDIM}`. Requested: {output_dim}"
)
base_samples = draw_sobol_normal_samples(
d=output_dim,
n=self.sample_shape.numel(),
device=posterior.device,
dtype=posterior.dtype,
seed=self.seed,
)
base_samples = base_samples.view(target_shape)
self.register_buffer("base_samples", base_samples)
self.to(device=posterior.device, dtype=posterior.dtype)
