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
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matlab工具箱可以直接计算：BessDerivZerosBisect2，besselzeros，getZerosBesselFunction
