def Distance(x, y, x0, y0):
    """
    Distance - returns the linear distance between 2 points

    Parameters
    ----------
        x: float or ndarray of floats
            x-coordinate of point1

        y: float or ndarray of floats
            y-coordinate of point1

        x0: float or ndarray of floats
            x-coordinate of point2

        y0: float or ndarray of floats
            y-coordinate of point2

    Returns
    -------
    return d
        d: float or ndarray of floats
            straight line distance between the 2 points

    N.B. all ndarrays must be the same size
    """
    d = ((x - x0) ** 2 + (y - y0) ** 2) ** 0.5
    return d
