def mse(predicted, actual):
diff = predicted - actual<EOL>return np.average(diff * diff, axis=<NUM_LIT:0>)<EOL>
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.