Check tri integral solution for Fourier Series

k=1:21;
c = 0.5*sinc(k/2).^2;
t = linspace(-0.5,0.5,401);
y = ones(size(t))*0.5;
for m = k
    y = y + 2*c(m)*cos(2*pi*m*t);
end
plot(t,y,'k','LineWidth',2);

plot error

ydiff = y - tri(2*t);
plot(t,ydiff);
[ymax idx] = max(ydiff);
fprintf('maximum error %g at t = %g\n',ymax,t(idx));

maximum error 0.00920469 at t = -0.5