add ARS to train/eval Minitaur

examples/pybullet/gym/pybullet_envs/ARS/optimizers.py

@@ -0,0 +1,35 @@
+# Code in this file is copied and adapted from
+# https://github.com/openai/evolution-strategies-starter.
+
+from __future__ import absolute_import
+from __future__ import division
+from __future__ import print_function
+
+import numpy as np
+
+# OPTIMIZERS FOR MINIMIZING OBJECTIVES
+class Optimizer(object):
+    def __init__(self, w_policy):
+        self.w_policy = w_policy.flatten()
+        self.dim = w_policy.size
+        self.t = 0
+
+    def update(self, globalg):
+        self.t += 1
+        step = self._compute_step(globalg)
+        ratio = np.linalg.norm(step) / (np.linalg.norm(self.w_policy) + 1e-5)
+        return self.w_policy + step, ratio
+
+    def _compute_step(self, globalg):
+        raise NotImplementedError
+
+
+class SGD(Optimizer):
+    def __init__(self, pi, stepsize):
+        Optimizer.__init__(self, pi)
+        self.stepsize = stepsize
+
+    def _compute_step(self, globalg):
+        step = -self.stepsize * globalg
+        return step
+