I need to take my trapezoid rule code and adjust it keeping the same format to Simpson rule

I need to take my trapezoid rule code and adjust it keeping the same format to Simpson rule. I am just no sure how to get this done. I have tried this and keep getting errors. Here is my trapezoid code. Thank You so much! function s = myTrap(f,a,b,n) x = linspace(a,b,n+1); %for n trapezoids, use n+1 points h = (b-a)/n; s = (f(a)+f(b))/2; %initialize sum %trap sum for i = 2:n s = s + f(x(i)); end s = s*h; %multiply sum by h when f= @(x)sqrt(1+x^3) from 1-4 with 20 traps I get 12.875041 for simpson the same function 1-4 should output 12.871490