from __future__ import annotations
import numpy as np
from smac.acquisition.function.abstract_acquisition_function import (
AbstractAcquisitionFunction,
)
from smac.utils.logging import get_logger
__copyright__ = "Copyright 2022, automl.org"
__license__ = "3-clause BSD"
logger = get_logger(__name__)
[docs]class TS(AbstractAcquisitionFunction):
r"""Thompson Sampling
Warning
-------
Thompson Sampling can only be used together with `RandomSearch`. Please do not use `LocalAndSortedRandomSearch` to
optimize the TS acquisition function!
:math:`TS(X) ~ \mathcal{N}(\mu(\mathbf{X}),\sigma(\mathbf{X}))'
Returns -TS(X) as the acquisition_function optimizer maximizes the acquisition value.
Parameters
----------
xi : float, defaults to 0.0
TS does not require xi here, we only wants to make it consistent with other acquisition functions.
"""
@property
def name(self) -> str: # noqa: D102
return "Thompson Sampling"
def _compute(self, X: np.ndarray) -> np.ndarray:
"""Sample a new value from a gaussian distribution whose mean and covariance values are given by model.
Parameters
----------
X: np.ndarray [N, D]
Points to be evaluated where we could sample a value. N is the number of points and D the dimension
for the points.
Returns
-------
np.ndarray [N, 1]
Negative sample value of X.
"""
assert self._model
if len(X.shape) == 1:
X = X[:, np.newaxis]
sample_function = getattr(self._model, "sample_functions", None)
if callable(sample_function):
return -sample_function(X, n_funcs=1)
m, var_ = self._model.predict_marginalized(X)
rng = self._model._rng
m = m.flatten()
var_ = np.diag(var_.flatten())
return -rng.multivariate_normal(m, var_, 1).T