add rewards examples

examples/rewards/forward_progress.py

@@ -0,0 +1,43 @@
+#!/usr/bin/env python
+"""Demonstrate how the reward function that measures how much a robot has moved forward increases / decreases based on
+the robot velocity. Use the arrow keys on your keyboard to move the robot, and observe how the computed reward value
+changes.
+"""
+
+from itertools import count
+import pyrobolearn as prl
+
+
+# Create simulator
+sim = prl.simulators.Bullet()
+
+# create world
+world = prl.worlds.BasicWorld(sim)
+
+# create wheeled robot
+robot = world.load_robot('epuck')
+
+# create interface and bridge to control the robot with the keyboard
+interface = prl.tools.interfaces.MouseKeyboardInterface()
+bridge = prl.tools.bridges.BridgeMouseKeyboardDifferentialWheeledRobot(robot=robot, interface=interface)
+
+# create state
+state = prl.states.BasePositionState(robot)
+
+# create reward
+reward = 1000 * prl.rewards.ForwardProgressReward(state=state, direction=(1, 0, 0))
+
+
+# run simulation
+for t in count():
+    # perform a step with the bridge and interface
+    bridge.step(update_interface=True)
+
+    # update state: in this case it will get the base position state and will save it in the state instance
+    state()
+
+    # compute reward: this will look in the previously given state instance its current state data
+    print("Reward value = {}".format(reward()))
+
+    # perform a step in the simulator
+    world.step(sim.dt)