import abc
import numpy as np
from ..utils import is_listlike
[docs]
class MoScalarFunction(abc.ABC):
"""Abstract class representing a scalarizing function.
Args:
n_objectives (int, optional): Number of objective functions. Defaults to ``1``.
weight (float or 1-D array, optional): Array of weights for each objective function. Defaults to ``None``.
weight_sampling_periode (int, optional): Sampling periode for the weight vector. Defaults to ``5``.
utopia_point (float or 1-D array, optional): Array of reference values for each objective function. Defaults to ``None``.
random_state (int, optional): Random seed. Defaults to ``None``.
"""
def __init__(
self,
n_objectives: int = 1,
weight=None,
weight_sampling_periode: int = 1,
utopia_point=None,
random_state=None,
):
self._seed = None
if type(random_state) is int:
self._seed = random_state
self._rng = np.random.RandomState(random_state)
elif isinstance(random_state, np.random.RandomState):
self._rng = random_state
else:
self._rng = np.random.RandomState()
if type(n_objectives) is not int:
raise ValueError("Parameter 'n_objectives' shoud be an integer value!")
self._n_objectives = n_objectives
self._utopia_point = None
if utopia_point is not None:
self._check_shape(utopia_point)
self._utopia_point = np.asarray(utopia_point)
# Record the passed weight vector.
self.weight = weight
self.weight_sampling_periode = weight_sampling_periode
self.counter_weight_sampling = -1
self._weight = None
self.update_weight()
def update_weight(self):
self.counter_weight_sampling += 1
if self.counter_weight_sampling % self.weight_sampling_periode != 0:
return
if self.weight == "random" or self.weight is None:
# Uniformly sample from the probability simplex using Remark 1.3
# from https://arxiv.org/pdf/1909.06406.pdf
# and the inverse exponential CDF: F_inv(p) = -log(1 - p).
# Can be checked with plot similar to Fig. 3 in http://www.cs.cmu.edu/~nasmith/papers/smith+tromble.tr04.pdf
self._weight = -np.log(1.0 - self._rng.rand(self._n_objectives))
self._weight /= np.sum(self._weight)
# self._weight = self._rng.dirichlet([1.0 for _ in range(self._n_objectives)])
elif self.weight == "uniform":
self._weight = np.ones(self._n_objectives) / self._n_objectives
elif is_listlike(self.weight):
self._check_shape(self.weight)
self._weight = np.asarray(self.weight)
else:
raise ValueError(f"Invalid weight value: {self.weight}")
def _check_shape(self, y):
"""Check if the shape of y is consistent with the object."""
if not (
(np.ndim(y) == 0 and self._n_objectives == 1)
or (np.ndim(y) == 1 and np.shape(y)[0] == self._n_objectives)
):
raise ValueError(
f"Expected y to be a scalar or 1-D array of length {self._n_objectives}"
)
[docs]
def scalarize(self, y):
"""Convert the input array (or scalar) into a scalar value.
Args:
yi (scalar or 1-D array): The input array or scalar to be scalarized.
Returns:
float: The converted scalar value.
"""
y = np.asarray(y)
return self._scalarize(y)
[docs]
def normalize(self, yi):
"""Compute normalization constants based on the history of evaluated objective values.
Args:
yi (array): Array of evaluated objective values.
Raises:
ValueError: Raised if yi is not a list of scalars each of length _n_objectives.
"""
if np.ndim(yi) != 2:
raise ValueError(f"Expected yi to be a 2D-array but is {yi}!")
self._utopia_point = np.min(yi, axis=0)
@abc.abstractmethod
def _scalarize(self, y):
"""Scalarization to be implemented.
Args:
y: Array of length _n_objectives.
Returns:
float: Converted scalar value.
"""
[docs]
class MoLinearFunction(MoScalarFunction):
"""This scalarizing function linearly combines the individual objective values (after automatically scaling them in [0, 1]).
Args:
n_objectives (int, optional): Number of objective functions. Defaults to ``1``.
weight (float or 1-D array, optional): Array of weights for each objective function. Defaults to ``None``.
weight_sampling_periode (int, optional): Sampling periode for the weight vector. Defaults to ``5``.
utopia_point (float or 1-D array, optional): Array of reference values for each objective function. Defaults to ``None``.
random_state (int, optional): Random seed. Defaults to ``None``.
"""
def __init__(
self,
n_objectives: int = 1,
weight=None,
weight_sampling_periode: int = 1,
utopia_point=None,
random_state=None,
):
super().__init__(
n_objectives, weight, weight_sampling_periode, utopia_point, random_state
)
def _scalarize(self, y):
return np.dot(self._weight, y)
[docs]
class MoChebyshevFunction(MoScalarFunction):
"""This scalarizing function computes a weighted infinity-norm of the individual objective values (after automatically scaling them in [0, 1]).
Args:
n_objectives (int, optional): Number of objective functions. Defaults to ``1``.
weight (float or 1-D array, optional): Array of weights for each objective function. Defaults to ``None``.
weight_sampling_periode (int, optional): Sampling periode for the weight vector. Defaults to ``5``.
utopia_point (float or 1-D array, optional): Array of reference values for each objective function. Defaults to ``None``.
random_state (int, optional): Random seed. Defaults to ``None``.
"""
def __init__(
self,
n_objectives: int = 1,
weight=None,
weight_sampling_periode: int = 1,
utopia_point=None,
random_state=None,
):
super().__init__(
n_objectives, weight, weight_sampling_periode, utopia_point, random_state
)
def _scalarize(self, y):
return np.max(np.multiply(self._weight, np.abs(y)))
[docs]
class MoPBIFunction(MoScalarFunction):
"""This scalarizing function computes the projection of the objective vector along a reference vector and adds a penalty term to minimize deviations from the projected point to the attainable objective set. See https://doi.org/10.1109/TEVC.2007.892759
Args:
n_objectives (int, optional): Number of objective functions. Defaults to ``1``.
weight (float or 1-D array, optional): Array of weights for each objective function. Defaults to ```None``.
weight_sampling_periode (int, optional): Sampling periode for the weight vector. Defaults to ``5``.
utopia_point (float or 1-D array, optional): Array of reference values for each objective function. Defaults to ``None``.
random_state (int, optional): Random seed. Defaults to ``None``.
penalty (float, optional): Value of penalty parameter. Defaults to ``100.0``.
"""
def __init__(
self,
n_objectives: int = 1,
weight=None,
weight_sampling_periode: int = 1,
utopia_point=None,
random_state=None,
penalty: float = 5.0,
):
self._penalty = np.abs(penalty) if np.isreal(penalty) else 5.0
super().__init__(
n_objectives, weight, weight_sampling_periode, utopia_point, random_state
)
def update_weight(self):
super().update_weight()
self._weightnorm = np.linalg.norm(self._weight) ** 2
def _scalarize(self, y):
d1 = np.dot(self._weight, y) / self._weightnorm
d2 = np.linalg.norm(y - (d1 * self._weight), 1)
return d1 + (self._penalty * d2)
[docs]
class MoAugmentedChebyshevFunction(MoScalarFunction):
"""This scalarizing function computes a sum of weighted infinity- and 1-norms of the individual objective values (after automatically scaling them in [0, 1]).
Args:
n_objectives (int, optional): Number of objective functions. Defaults to ``1``.
weight (float or 1-D array, optional): Array of weights for each objective function. Defaults to ``None``.
weight_sampling_periode (int, optional): Sampling periode for the weight vector. Defaults to ``5``.
utopia_point (float or 1-D array, optional): Array of reference values for each objective function. Defaults to ``None``.
random_state (int, optional): Random seed. Defaults to ``None``.
penalty (float, optional): Value of weight given to 1-norm. Defaults to ``0.001``.
"""
def __init__(
self,
n_objectives: int = 1,
weight=None,
weight_sampling_periode: int = 1,
utopia_point=None,
random_state=None,
alpha: float = 0.001,
):
self._alpha = np.abs(alpha) if np.isreal(alpha) else 0.001
super().__init__(
n_objectives, weight, weight_sampling_periode, utopia_point, random_state
)
def _scalarize(self, y):
y = np.multiply(self._weight, np.abs(y))
return np.max(y) + (self._alpha * np.linalg.norm(y, 1))
[docs]
class MoQuadraticFunction(MoScalarFunction):
"""This scalarizing function quadratically combines the individual objective values (after automatically scaling them in [0, 1]). It can be interpreted a smoother version of `MoChebyshevFunction`.
Args:
n_objectives (int, optional): Number of objective functions. Defaults to ``1``.
weight (float or 1-D array, optional): Array of weights for each objective function. Defaults to ``None``.
weight_sampling_periode (int, optional): Sampling periode for the weight vector. Defaults to ``5``.
utopia_point (float or 1-D array, optional): Array of reference values for each objective function. Defaults to ``None``.
random_state (int, optional): Random seed. Defaults to ``None``.
penalty (float, optional): Value of smoothness parameter. Larger values make it less smooth. Defaults to ``10.0``.
"""
def __init__(
self,
n_objectives: int = 1,
weight=None,
weight_sampling_periode: int = 1,
utopia_point=None,
random_state=None,
alpha: float = 10.0,
):
self._alpha = np.abs(alpha) if np.isreal(alpha) else 10.0
super().__init__(
n_objectives, weight, weight_sampling_periode, utopia_point, random_state
)
def update_weight(self):
super().update_weight()
U, _, _ = np.linalg.svd(self._weight.reshape(-1, 1), full_matrices=True)
self._Q = U.dot(
np.diag([self._alpha if j > 0 else 1.0 for j in range(self._n_objectives)])
).dot(U.T)
def _scalarize(self, y):
return y.T.dot(self._Q).dot(y)
