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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 _compute_standard_dev(self, rup, imt, C):
 """ Compute the the standard deviation in terms of magnitude described on page 744, eq. 4 """

        sigma_mean = 0.
        if imt.name in "SA PGA":
            psi = -6.898E-3
        else:
            psi = -3.054E-5
        if rup.mag <= 6.5:
            sigma_mean = (C['c12'] * rup.mag) + C['c13']
        elif rup.mag > 6.5:
            sigma_mean = (psi * rup.mag) + C['c14']
        return sigma_mean