%
%  m-file to illustrate simple interpolation and 
%  decimation operations (Program 9B.1, p641)
%	File name: prog9b1.m
%	An Illustration of interpolation by a factor of 4
%
Fs=1000;											%	sampling frequency
A=1.5;											%	relative amplitudes
B=1;
f1=50;											%	signal frequencies
f2=100;
t=0:1/Fs:1;										%	time vector
x=A*cos(2*pi*f1*t)+B*cos(2*pi*f2*t);	%	generate signal
y=interp(x,4);									%	interpolate signal by 4
stem(x(1:25))									%	plot original signal
xlabel('Discrete time, nT ')
ylabel('Input signal level')
figure
stem(y(1:100))									%	plot interpolated signal.
xlabel('Discrete time, 4 x nT')
ylabel('Output signal level')