p11.m

% p11.m - Chebyshev differentation of a smooth function
xx = -1:.01:1; uu = exp(xx).*sin(5*xx); clf
for N = [10 20]
[D,x] = cheb(N); u = exp(x).*sin(5*x);
subplot('position',[.15 .66-.4*(N==20) .31 .28])
plot(x,u,'.','markersize',14), grid on
line(xx,uu,'linewidth',.8)
title(['u(x), N=' int2str(N)])
error = D*u - exp(x).*(sin(5*x)+5*cos(5*x));
subplot('position',[.55 .66-.4*(N==20) .31 .28])
plot(x,error,'.','markersize',14), grid on
line(x,error,'linewidth',.8)
title([' error in u''(x), N=' int2str(N)])
end