运行到这一句“global xf=-gp.force.unbal_x(p_gp)*relax_m” 提示了如下错误 “FISH symbols cannot use a '.' character. From line 40 of source C:/Users/Administrator/Desktop/shanchu.txt. While processing line 11 of file C:/Users/Administrator/Desktop/shanchu.txt.” 望大佬解答