Random local search over a set of permissible values

cgp/local_search/random_search.py

@@ -0,0 +1,68 @@
+import numpy as np
+from typing import Callable
+
+
+class RandomLocalSearch:
+    def __init__(
+        self,
+        objective: Callable,
+        seed: int,
+        n_steps: int = 10,  # todo: should this be dependent on the number of parameters?
+        permissible_values: np.ndarray = np.logspace(start=0, stop=7, num=8, base=2, dtype=int),
+    ) -> None:
+        self.objective = objective
+        self.seed = seed
+        self.n_steps = n_steps
+        self.permissible_values = permissible_values
+
+    def __call__(self, ind) -> None:
+        rng = np.random.RandomState(self.seed)
+
+        params_values, params_names = ind.parameters_to_numpy_array(only_active_nodes=True)
+
+        if len(params_values) > 0:
+            for _ in range(self.n_steps):
+                # sample a new set of parameter values randomly
+                params_sampled = [
+                    rng.choice(self.permissible_values) for param_value in params_values
+                ]
+                # write the parameters into a clone of individual
+                new_ind = ind.clone()
+                new_ind.update_parameters_from_numpy_array(
+                    params=params_sampled, params_names=params_names
+                )
+                # evaluate fitness
+                self.objective(new_ind)
+                # if fitness improved: replace parameter values and fitness
+                if new_ind.fitness >= ind.fitness:  # todo: should this be >= or > ??
+                    ind.update_parameters_from_numpy_array(
+                        params=params_sampled, params_names=params_names
+                    )
+                    ind.fitness = new_ind.fitness
+
+
+if __name__ == "__main__":
+    import cgp
+
+    def objective(ind):
+        params_values, _ = ind.parameters_to_numpy_array(only_active_nodes=True)
+        ind.fitness = np.sum(params_values)
+        return ind
+
+    seed = 12345
+    genome = cgp.Genome(primitives=(cgp.Add, cgp.Sub, cgp.Mul, cgp.Parameter), n_inputs=1)
+    genome.randomize(rng=np.random.RandomState(seed=seed))
+    ind = cgp.IndividualSingleGenome(genome=genome)
+
+    objective(ind)
+    print(
+        f"Node parameters before local search "
+        f"{ind.parameters_to_numpy_array(only_active_nodes=True)} \n"
+    )
+
+    rls = RandomLocalSearch(objective=objective, seed=seed, n_steps=1000)
+    rls(ind)
+    print(
+        f"Node parameters after local search "
+        f"{ind.parameters_to_numpy_array(only_active_nodes=True)} \n"
+    )