Simpsons 1/3 rule using n =10 , 100, 1000

i cant get my code to work. im trying to implement the simpsons one-third rule to get the value of the certain function using n =10, 100, 1000. Any Help i would prefer to use the for loops.

%% Parameters
P = 5000; %lb 
a= 0; %lower bound 
b = 10; %upperbound
n = [10 100 1000]; % step size 

f = @(x) P / ((30e6)*(1-0.01*x-0.0005*x.^2)*2*exp(-0.1*x)); %function

%% Simpsons one-third rule 
for j = 1:length(n)
    h(j) = (b-a)/(n(j));
f_even = 0;
for i = 2:2:n-2 %even
    x = a+i *h(j);
    f_even = f_even + f(x);
end 
    f_odd = 0;
for i = 1:2:n-1 %odd
   x = a+i *h(j);
    f_odd = f_odd + f(x);
end 

I(j) = (h(j)/3) * (f(0) + 4* f_odd + 2*f_even +f(10)); %one-third rule
end

[Tommy]

One thing I noticed:

for i = 2:2:n-2 %even

Here, use

for i = 2:2:n(j)-2 %even

instead.

Same with

for i = 1:2:n-1 %odd

[Jose Puentes]

Thanks it worked !