Why do my loops only run once

function I=simpson13(f,a,b,n)
 
h=(b-a)/n; % length of the interval
total=0;
x=a;
fa=f; 
x=b;
fb=f;
 
for i=1:2:n-1;
   x=i*h;
   fn=f+total;
   total=fn;
end
 
for j=2:2:n-2;
   x=j*h;
   fm=f+total;
   total=fm;
end

I=(h/3)*(fa+fb+4*fn+2*fm);
end

[Raquel Terrer van Gool]

I have n=6:

x=0;
n=6; % n is the number of intervals and must be > 0 and even
a=0; b=pi;% a is the lower bound and b is the upper bound
f=5+13*sin(x); % Function
 
I=simpson13(f,a,b,n)

Answer 1

[Geoff Hayes]

Raquel - the MATLAB debugger is helpful in cases like this. If you put a breakpoint in your simpson13 you would notice a problem with the input parameter f. Look closely at how it is being assigned

x=0;
n=6; % n is the number of intervals and must be > 0 and even
a=0; b=pi;% a is the lower bound and b is the upper bound
f=5+13*sin(x); % Function

f is not a function in this case but is a scalar value (5) since x is zero. If you want f to be an anonymous function then you need to assign it as

f = @(x)5+13*sin(x);

where nthe @ operator creates the handle, and the parentheses () immediately after the @ operator include the function input arguments. You will need to change how this function is used in your code as well. For example,

fa=f(a); 
fb=f(b);

etc.

[Raquel Terrer van Gool]

I solved the problem with your help. Thank you very much!