Dt=0.00005;t=-0.005:Dt:0.005;xa=exp(-1000*abs(t));
Ts=0.0002;n=-25:1:25;x=exp(-1000*abs(n*Ts));
K=500;k=0:1:K;w=pi*k/K;
X=x*exp(-j*n'*w);X=real(X);
w=[-fliplr(w),w(2:K+1)];
X=[fliplr(X),X(2:K+1)]
subplot(1,1,1)
subplot(2,1,1);plot(t*1000,xa);
xlabel('t in msec');ylabel('x1(t)')
title('Discrete Signal'); hold on
stem(n*Ts*1000,x);gtext('Ts=0.2 msec'); hold off
subplot(2,1,2);plot(w/pi,X);
xlabel('Frequency in pi units');ylabel('X1(w)')
title('Discrete-time Fourier Transform')