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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 mse(predicted, actual):
 """ Mean squared error of predictions. .. versionadded:: 0.5.0 Parameters predicted : ndarray Predictions on which to measure error. May contain a single or multiple column but must match `actual` in shape. actual : ndarray Actual values against which to measure predictions. Returns ------- err : ndarray Mean squared error of predictions relative to actual values. """

    diff = predicted - actual
    return np.average(diff * diff, axis=0)