[MATLAB GUI] 新手求助啦，请各位帮我看看这个程序

[ppkeiko]

编了个程序，想实现
1.在地址栏输入文档名称，回车，即可以txt文档第一列为横坐标，第二列为纵坐标，在坐标系中画出曲线
2.点击右边的YMAX按钮，可在编辑栏显示该曲线y轴上的最大值

编来编去都不能实现第二个功能，请高手赐教，小妹谢过！

clf reset

H=axes('unit','normalized','position',[0,0,1,1],'visible','off');
set(gcf,'currentaxes',H);
str='test';
text(0.2,0.95,str,'fontsize',22);
h_fig=get(H,'parent');
set(h_fig,'unit','normalized','position',[0.1,0.1,0.5,0.5],'Toolbar','figure');
h_axes=axes('parent',h_fig,...
'unit','normalized','position',[0.1,0.1,0.6,0.6],...
'xlim',[-10 10],'ylim',[-10 10],'fontsize',8);

a_edit=uicontrol(h_fig,'style','edit',...
'unit','normalized','position',[0.1,0.83,0.4,0.06],...
'horizontal','left','callback',[...
'k=get(gcbo,''string'');,',...
'A=load(k);,',...
'a=A(:,1);,',...
'b=A(:,2);,',...
'hp=plot(a,b),hold on;,',...
'hold off;']);
ym_edit=uicontrol(h_fig,'style','edit','unit','normalized',...
'position',[0.7,0.6,0.3,0.05],'horizontal','left');
ym_push=uicontrol(h_fig,'style','push',...
'unit','normalized',...
'string','YMAX',...
'position',[0.7,0.8,0.3,0.05],...
'horizontal','left',...
'callback',[...
'bmm=max(b);,',...
'bmax=num2str(bmm);,',...
'set(ym_edit,"string",bmax);']);