Problem with for loop

areaneeded=3.75*100.1/100;
%disp(areaneeded) %area needed for a 0.1% error
a=1;
b=2;
for n=1:100;
    h=(b-a)/n;
    x=a:h:b;
    y=x.^3;
    ya=a.^3;
    yb=b.^3;
    area = h/2*(ya+yb+2*(sum(y)-ya-yb));
    %disp(area)
    tol=1e-12;
    if abs(areaneeded-area)<tol
        disp(n)
        break
    end
end
%

In this code i'm trying to find out the number of strips necessary to get an error of 0.1% with the trapezium rule. by cross multiplication i get the area i need to get with the trapezium rule, and then with the for loop i try to run n a hundred times (n=1, n=2, n=3...) and when the result from the trapezium rule is equal to the areaneeded display n. But i don't get any answer and i don't know how to solve it. Some help would be appreciate. Thanks in advance.

[per isakson]

Here your code runs without throwing any error. What error do you get?

[Alvaro García]

There was some kind of typing mistake on my code, now i dont get error but still i dont get any answers. Thanks in advance.

Answer 1

[Roger Stafford]

You have interpreted the phrase "get an error of 0.01%" far too literally. What is clearly meant is to find the smallest n such that the error is LESS than .01 percent of the correct amount. That means that you should write

   areaneeded = 3.75;  % The correct amount
   ....
   tol = 3.75*.0001;  % This is .01 percent of the correct amount
   ....
       if abs(areaneeded-area) < tol
         break;

As your code stands, the value n = 44 gets too much error and the next value n = 45 gets too little error to satisfy the tol = 1e-12 inequality which is a very tight requirement. Your code will never break.

[Alvaro García]

Thanks, i didnt notice that. Thanks a lot!