code: def std_ratio(sim=None, obs=None, node=None, skip_nan=False):
      
      sim, obs = prepare_arrays(sim, obs, node, skip_nan)
      return numpy.std(sim)/numpy.std(obs)-1.
docs: Calculate the ratio between the standard deviation of the simulated
      and the observed values.
  
      >>> from hydpy import round_
      >>> from hydpy import std_ratio
      >>> round_(std_ratio(sim=[1.0, 2.0, 3.0], obs=[1.0, 2.0, 3.0]))
      0.0
      >>> round_(std_ratio(sim=[1.0, 1.0, 1.0], obs=[1.0, 2.0, 3.0]))
      -1.0
      >>> round_(std_ratio(sim=[0.0, 3.0, 6.0], obs=[1.0, 2.0, 3.0]))
      2.0
  
      See the documentation on function |prepare_arrays| for some
      additional instructions for use of function |std_ratio|.