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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 frequency2fractional(frequency, mean_frequency=-1):
 """ Convert frequency in Hz to fractional frequency Parameters frequency: np.array Data array of frequency in Hz mean_frequency: float (optional) The nominal mean frequency, in Hz if omitted, defaults to mean frequency=np.mean(frequency) Returns ------- y: Data array of fractional frequency """

    if mean_frequency == -1:
        mu = np.mean(frequency)
    else:
        mu = mean_frequency
    y = [(x-mu)/mu for x in frequency]
    return y