axis('auto')
T=0.5;
delta = 0.1;

x = -1:delta:1;
y = 2*T*T*log(cosh(x/T));

dx = x;
dy = 2*T*tanh(x/T);

n = size(x);
n = n(2);
ddx = (x(1:n-1) + x(2:n))/2;
ddy = diff(dy)/delta;

plot(x,y)
axis([-1,1,0,1]);
pause

plot(dx,dy)
axis([-1,1,-1.25,1.25]);
pause

plot(ddx,ddy)

