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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 _interp_function(self, y_ip1, y_i, t_ip1, t_i, imt_per):
 """ Generic interpolation function used in equation 19 of 2013 report. """

        return y_i + (y_ip1 - y_i) / (t_ip1 - t_i) * (imt_per - t_i)