def double_norm(function, X1, X2):
    """
    Double normalization.

    Applies normalization function to two matrices.

    Parameters
    ----------
    function : function
    X1 : 1-st function input
    X2 : 2-nd function input

    Returns
    -------
    normed_X1, normed_X2 : 1-st function output, 2-nd function output
    """
    return function(X1), function(X2)