"""Provides the EvolutionStrategyEmitter."""
import numbers
import numpy as np
from ribs._utils import check_shape, validate_batch
from ribs.emitters._emitter_base import EmitterBase
from ribs.emitters.opt import _get_es
from ribs.emitters.rankers import _get_ranker
[docs]class EvolutionStrategyEmitter(EmitterBase):
"""Adapts a distribution of solutions with an ES.
This emitter originates in `Fontaine 2020
<https://arxiv.org/abs/1912.02400>`_. The multivariate Gaussian solution
distribution begins at ``x0`` with standard deviation ``sigma0``. Based on
how the generated solutions are ranked (see ``ranker``), the ES then adapts
the mean and covariance of the distribution.
Args:
archive (ribs.archives.ArchiveBase): An archive to use when creating
and inserting solutions. For instance, this can be
:class:`ribs.archives.GridArchive`.
x0 (np.ndarray): Initial solution. Must be 1-dimensional.
sigma0 (float): Initial step size / standard deviation of the
distribution from which solutions are sampled.
ranker (Callable or str): The ranker is a
:class:`~ribs.emitters.rankers.RankerBase` object that orders the
solutions after they have been evaluated in the environment. This
parameter may be a callable (e.g. a class or a lambda function) that
takes in no parameters and returns an instance of
:class:`~ribs.emitters.rankers.RankerBase`, or it may be a full or
abbreviated ranker name as described in
:mod:`ribs.emitters.rankers`.
es (Callable or str): The evolution strategy is an
:class:`~ribs.emitters.opt.EvolutionStrategyBase` object that is
used to adapt the distribution from which new solutions are sampled.
This parameter may be a callable (e.g. a class or a lambda function)
that takes in the parameters of
:class:`~ribs.emitters.opt.EvolutionStrategyBase` along with kwargs
provided by the ``es_kwargs`` argument, or it may be a full or
abbreviated optimizer name as described in :mod:`ribs.emitters.opt`.
es_kwargs (dict): Additional arguments to pass to the evolution
strategy optimizer. See the evolution-strategy-based optimizers in
:mod:`ribs.emitters.opt` for the arguments allowed by each
optimizer.
selection_rule ("mu" or "filter"): Method for selecting parents for the
evolution strategy. With "mu" selection, the first half of the
solutions will be selected as parents, while in "filter", any
solutions that were added to the archive will be selected.
restart_rule (int, "no_improvement", and "basic"): Method to use when
checking for restarts. If given an integer, then the emitter will
restart after this many iterations, where each iteration is a call
to :meth:`tell`. With "basic", only the default CMA-ES convergence
rules will be used, while with "no_improvement", the emitter will
restart when none of the proposed solutions were added to the
archive.
bounds (None or array-like): Bounds of the solution space. As suggested
in `Biedrzycki 2020
<https://www.sciencedirect.com/science/article/abs/pii/S2210650219301622>`_,
solutions are resampled until they fall within these bounds. Pass
None to indicate there are no bounds. Alternatively, pass an
array-like to specify the bounds for each dim. Each element in this
array-like can be None to indicate no bound, or a tuple of
``(lower_bound, upper_bound)``, where ``lower_bound`` or
``upper_bound`` may be None to indicate no bound.
batch_size (int): Number of solutions to return in :meth:`ask`. If not
passed in, a batch size will be automatically calculated using the
default CMA-ES rules.
seed (int): Value to seed the random number generator. Set to None to
avoid a fixed seed.
Raises:
ValueError: There is an error in x0 or initial_solutions.
ValueError: There is an error in the bounds configuration.
ValueError: If ``restart_rule``, ``selection_rule``, or ``ranker`` is
invalid.
"""
def __init__(
self,
archive,
*,
x0,
sigma0,
ranker="2imp",
es="cma_es",
es_kwargs=None,
selection_rule="filter",
restart_rule="no_improvement",
bounds=None,
batch_size=None,
seed=None,
):
EmitterBase.__init__(
self,
archive,
solution_dim=archive.solution_dim,
bounds=bounds,
)
seed_sequence = (seed if isinstance(seed, np.random.SeedSequence) else
np.random.SeedSequence(seed))
opt_seed, ranker_seed = seed_sequence.spawn(2)
self._x0 = np.array(x0, dtype=archive.dtype)
check_shape(self._x0, "x0", archive.solution_dim,
"archive.solution_dim")
self._sigma0 = sigma0
if selection_rule not in ["mu", "filter"]:
raise ValueError(f"Invalid selection_rule {selection_rule}")
self._selection_rule = selection_rule
self._restart_rule = restart_rule
self._restarts = 0
self._itrs = 0
# Check if the restart_rule is valid, discard check_restart result.
_ = self._check_restart(0)
self._opt = _get_es(
es,
sigma0=sigma0,
batch_size=batch_size,
solution_dim=self._solution_dim,
seed=opt_seed,
dtype=self.archive.dtype,
lower_bounds=self.lower_bounds,
upper_bounds=self.upper_bounds,
**(es_kwargs if es_kwargs is not None else {}),
)
self._opt.reset(self._x0)
self._ranker = _get_ranker(ranker, ranker_seed)
self._ranker.reset(self, archive)
self._batch_size = self._opt.batch_size
@property
def x0(self):
"""numpy.ndarray: Initial solution for the optimizer."""
return self._x0
@property
def batch_size(self):
"""int: Number of solutions to return in :meth:`ask`."""
return self._batch_size
@property
def restarts(self):
"""int: The number of restarts for this emitter."""
return self._restarts
@property
def itrs(self):
"""int: The number of iterations for this emitter, where each iteration
is a call to :meth:`tell`."""
return self._itrs
[docs] def ask(self):
"""Samples new solutions from a multivariate Gaussian.
The multivariate Gaussian is parameterized by the evolution strategy
optimizer ``self._opt``.
Returns:
(batch_size, :attr:`solution_dim`) array -- a batch of new solutions
to evaluate.
"""
return self._opt.ask()
def _check_restart(self, num_parents):
"""Emitter-side checks for restarting the optimizer.
The optimizer also has its own checks.
Args:
num_parents (int): The number of solution to propagate to the next
generation from the solutions generated by CMA-ES.
Raises:
ValueError: If :attr:`restart_rule` is invalid.
"""
if isinstance(self._restart_rule, numbers.Integral):
return self._itrs % self._restart_rule == 0
if self._restart_rule == "no_improvement":
return num_parents == 0
if self._restart_rule == "basic":
return False
raise ValueError(f"Invalid restart_rule {self._restart_rule}")
[docs] def tell(self, solution, objective, measures, add_info, **fields):
"""Gives the emitter results from evaluating solutions.
The solutions are ranked based on the `rank()` function defined by
`self._ranker`. Then, the ranked solutions are passed to CMA-ES for
adaptation.
This function also checks for restart condition and restarts CMA-ES
when needed.
Args:
solution (array-like): (batch_size, :attr:`solution_dim`) array of
solutions generated by this emitter's :meth:`ask()` method.
objective (array-like): 1D array containing the objective function
value of each solution.
measures (array-like): (batch_size, measure space dimension) array
with the measure space coordinates of each solution.
add_info (dict): Data returned from the archive
:meth:`~ribs.archives.ArchiveBase.add` method.
fields (keyword arguments): Additional data for each solution. Each
argument should be an array with batch_size as the first
dimension.
"""
data, add_info = validate_batch(
self.archive,
{
"solution": solution,
"objective": objective,
"measures": measures,
**fields,
},
add_info,
)
# Increase iteration counter.
self._itrs += 1
# Count number of new solutions.
new_sols = add_info["status"].astype(bool).sum()
# Sort the solutions using ranker.
indices, ranking_values = self._ranker.rank(self, self.archive, data,
add_info)
# Select the number of parents.
num_parents = (new_sols if self._selection_rule == "filter" else
self._batch_size // 2)
# Update Evolution Strategy.
self._opt.tell(indices, ranking_values, num_parents)
# Check for reset.
if (self._opt.check_stop(ranking_values[indices]) or
self._check_restart(new_sols)):
new_x0 = self.archive.sample_elites(1)["solution"][0]
self._opt.reset(new_x0)
self._ranker.reset(self, self.archive)
self._restarts += 1