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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def std_ratio(sim=None, obs=None, node=None, skip_nan=False):
 """Calculate the ratio between the standard deviation of the simulated and the observed values. 0.0 -1.0 2.0 See the documentation on function |prepare_arrays| for some additional instructions for use of function |std_ratio|. """

    sim, obs = prepare_arrays(sim, obs, node, skip_nan)
    return numpy.std(sim)/numpy.std(obs)-1.