plotsub2(f, a, b, n)

function plotsub2(f, a, b, n)

x =  linspace(a, b, n);
y =  feval(f, x); 
subplot('Position', [0.1, 0.4, 0.3, 0.3]); 
plot(x, y, 'y-'); 
title('\itfonction','fontsize',20);
subplot('Position', [0.5, 0.6, 0.3, 0.3]); 
yd =  diff(y)*n/(b-a); 
plot(x(1:end-1), yd, 'y-');
title('\itdrive','fontsize',20); 
axis([a,b,min(yd),max(yd)]);
subplot('Position', [0.5, 0.1, 0.3, 0.3]); 
yp =  (cumsum(y)-0.5*(y(1)-y))*(b-a)/n; 
plot(x, yp, 'y-');
title('\itprimitive','fontsize',20);
print -deps2 subplot2.eps