%  Sinc function weighting example steps through points of a sampled
%  rectangular pulse to interpolate points between existing points (based
%  on a higher sampling frequency). This demonstrates sinc weighting on
%  neighboring points to interpolate points between existing points.
%  In the graphics of this script notice the intersection of the sinc
%  with all the other existing samples, resulting in a weighted
%  contribution to the interpolated point.
%
%    written by Kevin D. Donohue (donohue@engr.uky.edu)  June 2002
%  Create discrete time axis for sampling signal
fs =5;
t = [-3*fs:3*fs]/fs;
%  Generate rectangular pulse
sig = rectpuls(t,1);   %  With width of 2 seconds centered on 0.


%  Create more densely sampled time axis for sinc function interpolator
fsc = fs*10;   %  Increase sampling rate by factor of 10
tc = [-3*fsc:3*fsc]/fsc;

%  Loop to slide sinc function along axis one FSC sample at a time
%  start just before middled of signal at t =0;
for k = fix(length(tc)/2):fix(length(tc)/2)+11
	stem(t,sig)  %  Plot stem plot of original signal at sample points
	hold on
	s = sinc((tc-tc(k))*fs);   %  Supperimpose sinc shifted by a submultiple of sampling increment
	plot(tc,s,'r', [tc(k) tc(k)], [0 1], 'g--')  %  Draw a green vertical line at interpolation point
    xlabel('Seconds')
    ylabel('Amplitude')
    title('Sinc function weights on surrounding points to interpolate at green broken line')
	axis([-1, 1, -.5, 1.1])  %  Limit axis around t=0 to get a better look
	hold off
	disp('Hit any key to continue')
    pause
end