最近搞了一下小程序，遇到点恶心的事情，特此记录，望帮助类似经历的难兄难弟少走一些弯路。

将教科书上的代码敲到了计算机上，运行发现如下错误：

Error while evaluating uicontrol Callback MATLAB GUI问题

Error: Missing variable or function.

??? Error while evaluating uicontrol Callback.

代码如下：

clear;
clf reset
H=axes('unit','normalized','position',[0,0,1,1],'visible','off');
set(gcf,'currentaxes',H);
str='\fontname {隶书} 归一化二阶系统的阶跃响应曲线';
text(0.12,0.93,str,'fontsize',13);
h_fig=get(H,'parent');
set(h_fig,'unit','normalized','position',[0.1,0.2,0.7,0.4]);
h_axes=axes('parent',h_fig,'unit','normalized','position',[0.1,0.15,0.55,0.7],'xlim',[0 15],'ylim',[0 1.8],'fontsize',8);

h_text=uicontrol(h_fig,'style','text','unit','normalized','position',[0.67,0.73,0.25,0.14],'horizontal','left','string',{'输入阻尼比系数','zeta='});

h_edit=uicontrol(h_fig,'style','edit','unit','normalized','position',[0.67,0.59,0.25,0.14],'horizontal','left','callback',['z=str2num(get(gcbo,''string''));', 't=0:0.1:15;','for k=1 :length(z);','y(:,k)=step(1,[1 2*z(k) 1],t);','plot(t,y(:,k));','if (length(z)>1) ,hold on ,end,','end;','hold off,']);

h_push1=uicontrol(h_fig,'style','push','unit','normalized','position',[0.67,0.37,0.12,0.15],'string','grid on','callback','grid on');

h_push2=uicontrol(h_fig,'style','push','unit','normalized','position',[0.67,0.15,0.12,0.15],'string','grid off','callback','grid off');
红色部分应该是两个单引号

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