syms x y;%定义符号
steps=str2num(get(handles.edit_steps,'string')) ;%获取阶数数组 if length(steps)==1%必须是单个曲线 switch get(handles.popupmenu_pick,'value')%获取贝塞尔函数的类型 case 1 y=besselj(steps(1),x); case 2 y=bessely(steps(1),x); end dy=diff(y);%一阶导函数 ddy=diff(dy);%二阶导函数 x=0.01:0.01:14; hold on; plot(x,subs(dy),'m'); plot(x,subs(ddy),'g'); hold off; end ———————————————— matlab工具箱可以直接计算：BessDerivZerosBisect2，besselzeros，getZerosBesselFunction
