I=2/3*( (2.5)^1.5-0.5^1.5 )

 % Gaussian-1 point: 
 I_m = 2*f(0),   I-I_m
 
 % Trap: 
 I_T = f(-1) + f(1),  I-I_T
 
 % Simpson:
 I_S = 2*(f(-1) + 4*f(0)+f(1))/6,  I-I_S
 
 % 2-pts Gaussian
 [x,w] = zplege(2);
 I_G2= w(1)*f(x(1)) + w(2)*f(x(2)),   I-I_G2
 
 [x,w] = zplege(3);
 I_G3= w(1)*f(x(1)) + w(2)*f(x(2))+w(3)*f(x(3)),   I-I_G3
 
 [x,w] = zplege(4); 
 I_G4 = 0;
 for j=1:4
     I_G4 =I_G4 +w(j)*f(x(j));
 end
 I_G4, I-I_G4
 
 n=6,
 [x,w] = zplege(6);
 I_G5 = 0;
 for j=1:n
     I_G5 =I_G5 +w(j)*f(x(j));
 end
 I_G5, I-I_G5