Matlab通过多项式拟合求贝塞尔函数的导函数

%产生拟合曲线，并求某点导数
% hObject    handle to btn_ployder (see GCBO)
% eventdata  reserved - to be defined in a future version of MATLAB
% handles    structure with handles and user data (see GUIDATA)
x=0.01:0.01:14;
steps=str2num(get(handles.edit_steps,"string")) ;
if length(steps)==1%必须是单个曲线
        switch get(handles.popupmenu_pick,"value")
            case 1          
                y=BESSELJ(steps(1),x);      
            case 2
                y=BESSELY(steps(1),x);        
        end
        a=polyfit(x,y,str2num(get(handles.edit_polyStep,"string")));%获取拟合多项式系数
        a1=polyder(a);%多项式一阶导数
        a2=polyder(a1);%多项式二阶导数
        t=polyval(a,x);
        hold on;
        plot(x,y,"b");%绘制贝塞尔曲线
        plot(x,t,"r:");%绘制拟合曲线
        hold off;
       
        xValue=str2num(get(handles.edit_xValue,"string")) ;
        yValue=polyval(a,xValue);%函数值
        dy1Value=polyval(a1,xValue);%一阶导数值
        dy2Value=polyval(a2,xValue);%二阶导数值
       
        set(handles.edit_yValue,"string",num2str(yValue));%显示
        set(handles.edit_dy1Value,"string",num2str(dy1Value));
        set(handles.edit_dy2Value,"string",num2str(dy2Value));
end