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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 get_eta(self, mag, std):
 """ Return Eta feature. Parameters mag : array_like An array of magnitudes. std : array_like A standard deviation of magnitudes. Returns ------- eta : float The value of Eta index. """


        diff = mag[1:] - mag[:len(mag) - 1]
        eta = np.sum(diff * diff) / (len(mag) - 1.) / std / std

        return eta