added balancing task

alr_envs/__init__.py

@@ -93,6 +93,15 @@ register(
     }
 )
 
+register(
+    id='Balancing-v0',
+    entry_point='alr_envs.mujoco:BalancingEnv',
+    max_episode_steps=200,
+    kwargs={
+        "n_links": 5,
+    }
+)
+
 register(
     id='SimpleReacher-v0',
     entry_point='alr_envs.classic_control:SimpleReacherEnv',

alr_envs/mujoco/__init__.py

@@ -1 +1,2 @@
-from alr_envs.mujoco.alr_reacher import ALRReacherEnv
+from alr_envs.mujoco.alr_reacher import ALRReacherEnv
+from alr_envs.mujoco.balancing import BalancingEnv

alr_envs/mujoco/balancing.py

@@ -0,0 +1,53 @@
+import os
+
+import numpy as np
+from gym import utils
+from gym.envs.mujoco import mujoco_env
+
+from alr_envs.utils.utils import angle_normalize
+
+
+class BalancingEnv(mujoco_env.MujocoEnv, utils.EzPickle):
+    def __init__(self, n_links=5):
+        utils.EzPickle.__init__(**locals())
+
+        self.n_links = n_links
+
+        if n_links == 5:
+            file_name = 'reacher_5links.xml'
+        elif n_links == 7:
+            file_name = 'reacher_7links.xml'
+        else:
+            raise ValueError(f"Invalid number of links {n_links}, only 5 or 7 allowed.")
+
+        mujoco_env.MujocoEnv.__init__(self, os.path.join(os.path.dirname(__file__), "assets", file_name), 2)
+
+    def step(self, a):
+        angle = angle_normalize(np.sum(self.sim.data.qpos.flat[:self.n_links]), type="rad")
+        reward = - np.abs(angle)
+
+        self.do_simulation(a, self.frame_skip)
+        ob = self._get_obs()
+        done = False
+        return ob, reward, done, dict(angle=angle, end_effector=self.get_body_com("fingertip").copy())
+
+    def viewer_setup(self):
+        self.viewer.cam.trackbodyid = 1
+
+    def reset_model(self):
+        # This also generates a goal, we however do not need/use it
+        qpos = self.np_random.uniform(low=-0.1, high=0.1, size=self.model.nq) + self.init_qpos
+        qpos[-2:] = 0
+        qvel = self.init_qvel + self.np_random.uniform(low=-.005, high=.005, size=self.model.nv)
+        qvel[-2:] = 0
+        self.set_state(qpos, qvel)
+
+        return self._get_obs()
+
+    def _get_obs(self):
+        theta = self.sim.data.qpos.flat[:self.n_links]
+        return np.concatenate([
+            np.cos(theta),
+            np.sin(theta),
+            self.sim.data.qvel.flat[:self.n_links],  # this is angular velocity
+        ])