%caiyang   演示采樣定理，時域采樣，頻譜周期延拓
%同時演示采樣頻率小于2*fc時，產生的混疊效應
clf reset
set(gcf,'unit','normalized','position',[0.1,0.2,0.5,0.5]);
set(gcf,'defaultuicontrolunits','normalized');
haxes1=axes('position',[0.05,0.2,0.4,0.2],...
            'xlim',[-5,5],'ylim',[-5,5]);
haxes2=axes('position',[0.5,0.2,0.4,0.2],...
            'xlim',[-1,1],'ylim',[0,1]);
haxes3=axes('position',[0.05,0.45,0.4,0.2],...
            'xlim',[-5,5],'ylim',[-5,5]);
haxes4=axes('position',[0.5,0.45,0.4,0.2],...
            'xlim',[-1,1],'ylim',[0,1]);
haxes5=axes('position',[0.05,0.7,0.4,0.2],...
            'xlim',[-20,20],'ylim',[-5,5]);
        %繪出初始時的時域信號
        t=-0.05:0.001:0.05;
        fc=100;   %這里假設三角波的頻帶寬度為100Hz
        y=fc/2*sinc(fc*t/4).*sinc(fc*t/4);
        plot(t,y);
        
haxes6=axes('position',[0.5,0.7,0.4,0.2],...
            'xlim',[-1,1],'ylim',[0,1.1]);
        %繪出頻譜
x1=1:-0.1:0;  x2=0:0.1:0.9;
x3=[x2,x1];
k=-10:10;
df=0.01;%這里假設fc=100,df代表10HZ 所以fc占用0.1
f=k*df;
plot(f,x3);axis([-1,1,0,1.1]);


htext1=uicontrol(gcf,'style','text',...
                 'position',[0.05,0.05,0.6,0.05],...
                 'backgroundcolor','white',...
                 'fontsize',10,...
                 'visible','on',...
                 'string','輸入采樣頻率（信號頻率為100Hz，100<fs<900)');
 htext2=uicontrol(gcf,'style','text',...
                 'position',[0.2,0.92,0.15,0.05],...
                 'fontsize',10,...
                 'string','時    域');
 htext3=uicontrol(gcf,'style','text',...
                  'position',[0.65,0.92,0.15,0.05],...
                  'fontsize',10,...
                  'string','頻   域');
 hedit=uicontrol('style','edit',...
                 'position',[0.7,0.05,0.2,0.05],...
                 'backgroundcolor','white',...
                 'visible','on');
 set(hedit,'CallBack',['call_caiyang1(haxes4);',...
             'call_caiyang3(haxes3);',...
             'call_caiyang4(haxes1,fc);',...
            'call_caiyang2(haxes2);']);