Simpson's 1/3 rules

Hi,

I am not sure why this does not work.Should I replace the i with j?I appreciate any help.

function I=mysimp(f,a,b,n)
h=(b-a)/n;
sum4=0;
sum2=0;
for i=2:2:n
    x(i)=a+i*h;
    y(i)=f(x(i))
    sum4=sum4+4*feval(f,x(i));
end
    if i=3:2:n-1;
       x(i)=a+i*h;
    y(i)=f(x(i))
    sum2=sum2+2*feval(f,x(i));
    end
    sum=sum2+sum4+feval(f,a)+feval(f,b);
    I=sum*h/3;
    plot(x,y)

this is what I get

Error: File: mysimp.m Line: 10 Column: 9
The expression to the left of the equals sign is not a valid target for an assignment.

Answer 1

[John D'Errico]

A TERRIBLE idea to use the name sum as a variable. You WILL get int trouble later on if you continue to use incredibly useful function names as variable names too. And then your anquished question will be WHAT IS WRONG WITH MY CODE????

Regardless, the following line is not valid syntax in MATLAB:

 if i=3:2:n-1;

[Nasser Yari]

Thanks for the advice. I found out where I made a typo mistake if should be for.