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)
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.