def read_file(filename):
    """ 'filename' should be a two column file. This
        function will return, as two lists, the first and second column of this file.
    """
    x, y = [], []
    with open(filename, "r") as f:
        for l in f:
            if l[0] != "#":
                l = l.split()
                x.append(float(l[0]))
                y.append(float(l[1]))

        return x, y