Matlab直接求贝塞尔函数的导函数

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