Fix differential evolution (#1150)

* Fix differential evolution

* Update CHANGELOG.md

* Vectorize diff evo

* Add test for categorical search space

* Formatting

* Remove unused imports

* Another formatting fix

CHANGELOG.md

@@ -15,6 +15,9 @@
 ## Dependencies
 - Allow numpy >= 2.x (#1146)
 
+## Bugfixes
+- Fix bug in differential evolution acquisition maximizer in case the search space contains categorical hyperparameters (#1150)
+
 # Examples
 - Add warmstarting example (#1120)
 

smac/acquisition/maximizer/differential_evolution.py

@@ -1,10 +1,14 @@
 from __future__ import annotations
 
 import numpy as np
-from ConfigSpace import Configuration
+from ConfigSpace import Configuration, ConfigurationSpace
 from scipy.optimize._differentialevolution import DifferentialEvolutionSolver
 
+from smac.acquisition.function.abstract_acquisition_function import (
+    AbstractAcquisitionFunction,
+)
 from smac.acquisition.maximizer import AbstractAcquisitionMaximizer
+from smac.utils.configspace import transform_continuous_designs
 
 __copyright__ = "Copyright 2022, automl.org"
 __license__ = "3-clause BSD"
@@ -23,8 +27,46 @@ class DifferentialEvolution(AbstractAcquisitionMaximizer):
 
     [1] Storn, R and Price, K, Differential Evolution - a Simple and Efficient Heuristic for Global
      Optimization over Continuous Spaces, Journal of Global Optimization, 1997, 11, 341 - 359.
+
+    Parameters
+    ----------
+    configspace : ConfigurationSpace
+    acquisition_function : AbstractAcquisitionFunction
+    challengers : int, defaults to 50000
+        Number of challengers.
+    max_iter: int | None, defaults to None
+        Maximum number of iterations that the DE will perform.
+    strategy: str, defaults to "best1bin"
+        The strategy to use for the DE.
+    polish: bool, defaults to True
+        Whether to polish the final solution using L-BFGS-B.
+    mutation: tuple[float, float], defaults to (0.5, 1.0)
+        The mutation constant.
+    recombination: float, defaults to 0.7
+        The recombination constant.
+    seed : int, defaults to 0
     """
 
+    def __init__(
+        self,
+        configspace: ConfigurationSpace,
+        acquisition_function: AbstractAcquisitionFunction | None = None,
+        max_iter: int = 1000,
+        challengers: int = 50000,
+        strategy: str = "best1bin",
+        polish: bool = True,
+        mutation: tuple[float, float] = (0.5, 1.0),
+        recombination: float = 0.7,
+        seed: int = 0,
+    ):
+        super().__init__(configspace, acquisition_function, challengers, seed)
+        # raise NotImplementedError("DifferentialEvolution is not yet implemented.")
+        self.max_iter = max_iter
+        self.strategy = strategy
+        self.polish = polish
+        self.mutation = mutation
+        self.recombination = recombination
+
     def _maximize(
         self,
         previous_configs: list[Configuration],
@@ -36,30 +78,46 @@ def _maximize(
 
         def func(x: np.ndarray) -> np.ndarray:
             assert self._acquisition_function is not None
-            return -self._acquisition_function([Configuration(self._configspace, vector=x)])
+            if len(x.shape) == 1:
+                return -self._acquisition_function(
+                    [
+                        transform_continuous_designs(
+                            design=np.expand_dims(x, axis=0),
+                            origin="Diffrential Evolution",
+                            configspace=self._configspace,
+                        )[0]
+                    ]
+                )
+            return -self._acquisition_function(
+                transform_continuous_designs(design=x.T, origin="Diffrential Evolution", configspace=self._configspace)
+            )
 
         ds = DifferentialEvolutionSolver(
             func,
             bounds=[[0, 1] for _ in range(len(self._configspace))],
             args=(),
-            strategy="best1bin",
-            maxiter=1000,
-            popsize=50,
+            strategy=self.strategy,
+            maxiter=self.max_iter,
+            popsize=self._challengers // self.max_iter,
             tol=0.01,
-            mutation=(0.5, 1),
-            recombination=0.7,
+            mutation=self.mutation,
+            recombination=self.recombination,
             seed=self._rng.randint(1000),
-            polish=True,
+            polish=self.polish,
             callback=None,
             disp=False,
             init="latinhypercube",
             atol=0,
+            vectorized=True,
         )
 
         _ = ds.solve()
         for pop, val in zip(ds.population, ds.population_energies):
-            rc = Configuration(self._configspace, vector=pop)
-            rc.origin = "Acquisition Function Maximizer: Differential Evolution"
+            rc = transform_continuous_designs(
+                design=np.expand_dims(pop, axis=0),
+                origin="Acquisition Function Maximizer: Differential Evolution",
+                configspace=self._configspace,
+            )[0]
             configs.append((-val, rc))
 
         configs.sort(key=lambda t: t[0])

smac/initial_design/abstract_initial_design.py

@@ -6,15 +6,7 @@
 from collections import OrderedDict
 
 import numpy as np
-from ConfigSpace.configuration_space import Configuration, ConfigurationSpace
-from ConfigSpace.hyperparameters import (
-    CategoricalHyperparameter,
-    Constant,
-    IntegerHyperparameter,
-    NumericalHyperparameter,
-    OrdinalHyperparameter,
-)
-from ConfigSpace.util import ForbiddenValueError, deactivate_inactive_hyperparameters
+from ConfigSpace.configuration_space import Configuration
 
 from smac.scenario import Scenario
 from smac.utils.logging import get_logger
@@ -155,57 +147,3 @@ def select_configurations(self) -> list[Configuration]:
     def _select_configurations(self) -> list[Configuration]:
         """Selects the initial configurations, depending on the implementation of the initial design."""
         raise NotImplementedError
-
-    def _transform_continuous_designs(
-        self, design: np.ndarray, origin: str, configspace: ConfigurationSpace
-    ) -> list[Configuration]:
-        """Transforms the continuous designs into a discrete list of configurations.
-
-        Parameters
-        ----------
-        design : np.ndarray
-            Array of hyperparameters originating from the initial design strategy.
-        origin : str | None, defaults to None
-            Label for a configuration where it originated from.
-        configspace : ConfigurationSpace
-
-        Returns
-        -------
-        configs : list[Configuration]
-            Continuous transformed configs.
-        """
-        params = list(configspace.values())
-        for idx, param in enumerate(params):
-            if isinstance(param, IntegerHyperparameter):
-                design[:, idx] = param.to_vector(param.to_value(design[:, idx]))
-            elif isinstance(param, NumericalHyperparameter):
-                continue
-            elif isinstance(param, Constant):
-                design_ = np.zeros(np.array(design.shape) + np.array((0, 1)))
-                design_[:, :idx] = design[:, :idx]
-                design_[:, idx + 1 :] = design[:, idx:]
-                design = design_
-            elif isinstance(param, CategoricalHyperparameter):
-                v_design = design[:, idx]
-                v_design[v_design == 1] = 1 - 10**-10
-                design[:, idx] = np.array(v_design * len(param.choices), dtype=int)
-            elif isinstance(param, OrdinalHyperparameter):
-                v_design = design[:, idx]
-                v_design[v_design == 1] = 1 - 10**-10
-                design[:, idx] = np.array(v_design * len(param.sequence), dtype=int)
-            else:
-                raise ValueError("Hyperparameter not supported when transforming a continuous design.")
-
-        configs = []
-        for vector in design:
-            try:
-                conf = deactivate_inactive_hyperparameters(
-                    configuration=None, configuration_space=configspace, vector=vector
-                )
-            except ForbiddenValueError:
-                continue
-
-            conf.origin = origin
-            configs.append(conf)
-
-        return configs

smac/initial_design/latin_hypercube_design.py

@@ -5,6 +5,7 @@
 from scipy.stats.qmc import LatinHypercube
 
 from smac.initial_design.abstract_initial_design import AbstractInitialDesign
+from smac.utils.configspace import transform_continuous_designs
 
 __copyright__ = "Copyright 2022, automl.org"
 __license__ = "3-clause BSD"
@@ -25,6 +26,6 @@ def _select_configurations(self) -> list[Configuration]:
 
         lhd = LatinHypercube(d=len(params) - constants, seed=self._rng.randint(0, 1000000)).random(n=self._n_configs)
 
-        return self._transform_continuous_designs(
+        return transform_continuous_designs(
             design=lhd, origin="Initial Design: Latin Hypercube", configspace=self._configspace
         )

smac/initial_design/sobol_design.py

@@ -9,6 +9,7 @@
 from scipy.stats.qmc import Sobol
 
 from smac.initial_design.abstract_initial_design import AbstractInitialDesign
+from smac.utils.configspace import transform_continuous_designs
 
 __copyright__ = "Copyright 2022, automl.org"
 __license__ = "3-clause BSD"
@@ -43,6 +44,4 @@ def _select_configurations(self) -> list[Configuration]:
             warnings.simplefilter("ignore")
             sobol = sobol_gen.random(self._n_configs)
 
-        return self._transform_continuous_designs(
-            design=sobol, origin="Initial Design: Sobol", configspace=self._configspace
-        )
+        return transform_continuous_designs(design=sobol, origin="Initial Design: Sobol", configspace=self._configspace)

smac/utils/configspace.py

@@ -11,13 +11,19 @@
     BetaIntegerHyperparameter,
     CategoricalHyperparameter,
     Constant,
+    IntegerHyperparameter,
     NormalFloatHyperparameter,
     NormalIntegerHyperparameter,
+    NumericalHyperparameter,
     OrdinalHyperparameter,
     UniformFloatHyperparameter,
     UniformIntegerHyperparameter,
 )
-from ConfigSpace.util import get_one_exchange_neighbourhood
+from ConfigSpace.util import (
+    ForbiddenValueError,
+    deactivate_inactive_hyperparameters,
+    get_one_exchange_neighbourhood,
+)
 
 __copyright__ = "Copyright 2022, automl.org"
 __license__ = "3-clause BSD"
@@ -182,6 +188,61 @@ def print_config_changes(
     logger.debug(msg)
 
 
+def transform_continuous_designs(
+    design: np.ndarray, origin: str, configspace: ConfigurationSpace
+) -> list[Configuration]:
+    """Transforms the continuous designs into a discrete list of configurations.
+
+    Parameters
+    ----------
+    design : np.ndarray
+        Array of hyperparameters originating from the initial design strategy.
+    origin : str | None, defaults to None
+        Label for a configuration where it originated from.
+    configspace : ConfigurationSpace
+
+    Returns
+    -------
+    configs : list[Configuration]
+        Continuous transformed configs.
+    """
+    params = configspace.get_hyperparameters()
+    for idx, param in enumerate(params):
+        if isinstance(param, IntegerHyperparameter):
+            design[:, idx] = param._inverse_transform(param._transform(design[:, idx]))
+        elif isinstance(param, NumericalHyperparameter):
+            continue
+        elif isinstance(param, Constant):
+            design_ = np.zeros(np.array(design.shape) + np.array((0, 1)))
+            design_[:, :idx] = design[:, :idx]
+            design_[:, idx + 1 :] = design[:, idx:]
+            design = design_
+        elif isinstance(param, CategoricalHyperparameter):
+            v_design = design[:, idx]
+            v_design[v_design == 1] = 1 - 10**-10
+            design[:, idx] = np.array(v_design * len(param.choices), dtype=int)
+        elif isinstance(param, OrdinalHyperparameter):
+            v_design = design[:, idx]
+            v_design[v_design == 1] = 1 - 10**-10
+            design[:, idx] = np.array(v_design * len(param.sequence), dtype=int)
+        else:
+            raise ValueError("Hyperparameter not supported when transforming a continuous design.")
+
+    configs = []
+    for vector in design:
+        try:
+            conf = deactivate_inactive_hyperparameters(
+                configuration=None, configuration_space=configspace, vector=vector
+            )
+        except ForbiddenValueError:
+            continue
+
+        conf.origin = origin
+        configs.append(conf)
+
+    return configs
+
+
 # def check_subspace_points(
 #     X: np.ndarray,
 #     cont_dims: np.ndarray | list = [],