fc=100;
qifs=10*fc;
t = (0:qifs-1)/qifs;
%x = sin(2*pi*50*t) + sin(2*pi*150*t)+sin(2*pi*100*t);
x=zeros(qifs); % input signal
x(1)=1;
X = fft(x);
X = abs(X);
X=X(1:qifs/2+1);
f=0:qifs/2;
figure(1); % display the input signal
subplot(2,1,1);
plot(f,X); % frequency domain
title('Input signal in Frequency Domain');
ylabel('Magnitude'); xlabel('f/Hz');
subplot(2,1,2);
plot(t,x); % time domain
title('Input signal In Time Domain');
ylabel('Magnitude'); xlabel('T/s');
[a,b]=butter(8,fc/(qifs/2)); %IIR filter design
y=filter(a,b,x);
Y=fft(y);
Y=abs(Y);
Y=Y(1:qifs/2+1);
figure(2); %display the output signal
subplot(2,1,1); %frequency domain
plot(f,Y);
title('Output signal in Frequency Domain');
ylabel('Magnitude'); xlabel('f/Hz');
subplot(2,1,2); % time domain
plot(t,y);
title('Output signal in Frequency Domain');
ylabel('Magnitude'); xlabel('T/s');
