code: def bias_abs(sim=None, obs=None, node=None, skip_nan=False):
      
      sim, obs = prepare_arrays(sim, obs, node, skip_nan)
      return numpy.mean(sim-obs)
docs: Calculate the absolute difference between the means of the simulated
      and the observed values.
  
      >>> from hydpy import round_
      >>> from hydpy import bias_abs
      >>> round_(bias_abs(sim=[2.0, 2.0, 2.0], obs=[1.0, 2.0, 3.0]))
      0.0
      >>> round_(bias_abs(sim=[5.0, 2.0, 2.0], obs=[1.0, 2.0, 3.0]))
      1.0
      >>> round_(bias_abs(sim=[1.0, 1.0, 1.0], obs=[1.0, 2.0, 3.0]))
      -1.0
  
      See the documentation on function |prepare_arrays| for some
      additional instructions for use of function |bias_abs|.