test_turtlebot.py: addition on lists throws TypeError

[abhishek47kashyap]

python -m examples.test_turtlebot crashes due to this TypeError:

Traceback (most recent call last):
  File "/usr/lib/python3.8/runpy.py", line 194, in _run_module_as_main
    return _run_code(code, main_globals, None,
  File "/usr/lib/python3.8/runpy.py", line 87, in _run_code
    exec(code, run_globals)
  File "/home/abhishek/pybullet-planning/examples/test_turtlebot.py", line 98, in <module>
    main()
  File "/home/abhishek/pybullet-planning/examples/test_turtlebot.py", line 84, in main
    center = (lower + upper)/2. # Computing the center of the AABB
TypeError: unsupported operand type(s) for /: 'list' and 'float'

pybullet-planning/examples/test_turtlebot.py

Lines 82 to 84 in d536384

	robot_aabb = get_subtree_aabb(robot, base_link) # Computes the robot's axis-aligned bounding box (AABB)
	lower, upper = robot_aabb # Decomposing the AABB into the lower and upper extrema
	center = (lower + upper)/2. # Computing the center of the AABB

Since lower and upper are both type list, adding them results in concatenation instead of element-wise addition.

[yasminedaly]

Do this and it should work just fine

lower = np.array(lower)
upper = np.array(upper)
center = (lower + upper) / 2.0