Dynamics randomization for MuJoCo (#51)

Add support for dynamics randomization for mujoco environment.
Includes a simple data structure consisting of a list of variation
objects, a wrapped environment of mujoco to perform dynamics
randomization.
Each variation object is an instance of the Variation class
that works as a container for each of the fields used to randomized a
dynamic parameter within the simulation environment.
The wrapper class of mujoco performs dynamics randomization on each
reset().
The data structure and the wrapper class are tested in
test_dynamics_rand.py.

Refer to: #14

rllab/envs/mujoco/randomization/__init__.py

@@ -0,0 +1,4 @@
+from rllab.envs.mujoco.randomization.randomized_env import randomize
+from rllab.envs.mujoco.randomization.variation import Distribution
+from rllab.envs.mujoco.randomization.variation import Method
+from rllab.envs.mujoco.randomization.variation import Variations

rllab/envs/mujoco/randomization/randomized_env.py

@@ -0,0 +1,81 @@
+import os.path as osp
+
+from mujoco_py import load_model_from_xml
+from mujoco_py import MjSim
+
+from rllab.core import Serializable
+from rllab.envs import Env
+from rllab.envs.mujoco.mujoco_env import MODEL_DIR
+
+
+class RandomizedEnv(Env, Serializable):
+    """
+    This class is just a wrapper class for the MujocoEnv to perform
+    the training using Dynamics Randomization.
+    Only code in the methods reset and terminate has been added.
+    """
+
+    def __init__(self, mujoco_env, variations):
+        """
+        Set variations with the node in the XML file at file_path.
+        """
+        Serializable.quick_init(self, locals())
+        self._wrapped_env = mujoco_env
+        self._variations = variations
+        self._file_path = osp.join(MODEL_DIR, mujoco_env.FILE)
+        self._variations.initialize_variations(self._file_path)
+
+    def reset(self):
+        """
+        The new model with randomized parameters is requested and the
+        corresponding parameters in the MuJoCo environment class are
+        set.
+        """
+        self._wrapped_env.model = load_model_from_xml(
+            self._variations.get_randomized_xml_model())
+        if hasattr(self._wrapped_env, 'action_space'):
+            del self._wrapped_env.__dict__['action_space']
+        self._wrapped_env.sim = MjSim(self._wrapped_env.model)
+        self._wrapped_env.data = self._wrapped_env.sim.data
+        self._wrapped_env.init_qpos = self._wrapped_env.sim.data.qpos
+        self._wrapped_env.init_qvel = self._wrapped_env.sim.data.qvel
+        self._wrapped_env.init_qacc = self._wrapped_env.sim.data.qacc
+        self._wrapped_env.init_ctrl = self._wrapped_env.sim.data.ctrl
+        return self._wrapped_env.reset()
+
+    def step(self, action):
+        return self._wrapped_env.step(action)
+
+    def render(self, *args, **kwargs):
+        return self._wrapped_env.render(*args, **kwargs)
+
+    def log_diagnostics(self, paths, *args, **kwargs):
+        self._wrapped_env.log_diagnostics(paths, *args, **kwargs)
+
+    def get_param_values(self):
+        return self._wrapped_env.get_param_values()
+
+    def set_param_values(self, params):
+        self._wrapped_env.set_param_values(params)
+
+    def terminate(self):
+        self._wrapped_env.terminate()
+
+    @property
+    def wrapped_env(self):
+        return self._wrapped_env
+
+    @property
+    def action_space(self):
+        return self._wrapped_env.action_space
+
+    @property
+    def observation_space(self):
+        return self._wrapped_env.observation_space
+
+    @property
+    def horizon(self):
+        return self._wrapped_env.horizon
+
+
+randomize = RandomizedEnv