% spline_sine.m generates a coarse sine curve, then interpolates with splines

x = 0:12;                  % set up x data points, x=(0 1 2 3 ... 10)
y = sin(x);                % set up y data points

subplot(3,1,1)             % this is the first of three plots
plot(x,y,'o')
title('Data points from sine curve');
axis([min(x) max(x) -1.5 1.5]);

xi = 0:.05:12;             % x values for interpolation - finer than x
yi = spline(x,y,xi);       % interpolated y values

subplot(3,1,2)             % this is the second of three plots
plot(x,y,'o',xi,yi)        % plot data points and interpolated curve
title('Data points and interpolating spline');
axis([min(x) max(x) -1.5 1.5]);

yt = sin(xi);              % values of y according to the sine function

subplot(3,1,3)             % this is the third of three plots
plot(xi,yt-yi);            % the difference between the true and interpolated
title('Difference between interpolation and actual sine curve');