docs: def radialAverage(arr, center=None):
      """
      radial average a 2darray around a center
      if no center is given, take middle
      """
      # taken from
      # http://stackoverflow.com/questions/21242011/most-efficient-way-to-calculate-radial-profile
      s0, s1 = arr.shape[:2]
      if center is None:
          center = s0/2, s1/2
      y, x = np.indices((s0, s1))
      r = np.sqrt((x - center[0])**2 + (y - center[1])**2)
      r = r.astype(np.int)
      tbin = np.bincount(r.ravel(), arr.ravel())
      nr = np.bincount(r.ravel())
      radialprofile = tbin/ nr
      return radialprofile