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% exa090203.m,   for figure 9.2.3 
%------------------------------------------------------------------------ 
 
T=8; 
w0=2; 
%---------NO.1--------- 
t=-2*pi:0.01:2*pi; 
g=exp(-t.^2/T).*cos(w0*t); 
gg=exp(-t.^2/T); 
subplot(2,2,1); 
plot(t,g,'-k'); 
hold on; 
plot(t,gg,'--k'); 
%-------plot the X axis 
zer_x=-10:1:10; 
zer_xx=zeros(size(zer_x)); 
plot(zer_x,zer_xx,'-k'); 
text(10,-0.1,'t'); 
%------plot the Y axis 
zer_yy=-1:0.5:1.5; 
zer_y=0*ones(size(zer_yy)); 
plot(zer_y,zer_yy,'-k'); 
axis([-10,10,-1,1.5]); 
axis('off'); 
 
%-------NO.2------ 
w=-2*pi:0.01:2*pi; 
G=sqrt(pi/T)*exp(-(w-w0).^2/(4/T)); 
subplot(2,2,2); 
plot(w,G,'-k'); 
hold on; 
%--------plot the X axis 
zer_x=0:1:4; 
zer_xx=zeros(size(zer_x)); 
plot(zer_x,zer_xx,'-k'); 
%--------plot the Y axis 
zer_yy=0:0.5:1; 
zer_y=0*ones(size(zer_yy)); 
plot(zer_y,zer_yy,'-k'); 
%--------plot the axis! 
zer_ww=0:0.5:max(G); 
zer_w=w0*ones(size(zer_ww)); 
plot(zer_w,zer_ww,'--k'); 
axis([0,4,0,1]); 
axis('off'); 
 
%---------NO.3--------- 
t=-2*pi:0.01:2*pi; 
g=exp(-t.^2/T).*cos(2*w0*t); 
gg=exp(-t.^2/T); 
subplot(2,2,3); 
plot(t,g,'-k'); 
hold on; 
plot(t,gg,'--k'); 
%--------plot the X axis 
zer_x=-10:1:10; 
zer_xx=zeros(size(zer_x)); 
plot(zer_x,zer_xx,'-k'); 
text(10,-0.1,'t'); 
%--------plot the Y axis 
zer_yy=-1:0.5:1.5; 
zer_y=0*ones(size(zer_yy)); 
plot(zer_y,zer_yy,'-k'); 
axis([-10,10,-1,1.5]); 
axis('off'); 
 
%-------NO.4------ 
w=-2*pi:0.01:2*pi; 
G4=sqrt(pi/T)*exp(-(w-2*w0).^2/(4/T)); 
subplot(2,2,4); 
plot(w,G4,'-k'); 
hold on; 
%---------plot the X axis! 
zer_x=0:1:6; 
zer_xx=zeros(size(zer_x)); 
plot(zer_x,zer_xx,'-k'); 
%---------plot the Y axis! 
zer_yy=0:0.5:1; 
zer_y=0*ones(size(zer_yy)); 
plot(zer_y,zer_yy,'-k'); 
%---------plot the axis! 
zer_ww=0:0.5:max(G4); 
zer_w=2*w0*ones(size(zer_ww)); 
plot(zer_w,zer_ww,'--k'); 
axis([0,6,0,1]); 
axis('off');