def py_static(y, pu, yc):
    """
    Static p-y model developed by Matlock
    
    Parameters
    ----------------
    y -- displacement
    pu -- ultimate stress
    yc -- ultimate displacement
    
    Output
    ----------------
    p -- soil resistence pressure
    """
    if y / yc <= 8:
        p = 0.5 * pu * (y / yc) ** (1 / 3)
    else:
        p = pu
    return p
