Can anyone help me with this code? I want to find the x(n) that has an Error smaller than Criteria. The code seems never stop and I don't know what's wrong with my code. Thanks

Criteria = 2*rand;
y = @(x) 0.1.*x.^4-2.*x.^3+8.*x.^2+10.*cos(x);
dydx = @(x) 0.4.*x.^3-6.*x.^2+16.*x-10.*sin(x);
x1 = 5;
    x2 = x1-y(x1)./dydx(x1);
    Error = 100.*abs(x2-x1)./x2;
    x(1) = 5;
for n = 2:4
    while Error >= Criteria
    x(n) = x(n-1)-y(x(n-1))./dydx(x(n-1));
    Error(n) = 100.*abs(x(n) - x(n-1))./x(n);
    end
    BestGuess = x(n);
end 

Answer 1

[Walter Roberson]

You assign to Error(n), so we can see that Error is expected to be a vector. But your while loop is

while Error >= Criteria

We just established that Error is expected to be a vector, so this is a vector test of all elements in Error to Criteria. When you use a vector of values in if or while the test is considered true only if all the tests are true. If there is any element in Error which is < Criteria then the loop would stop. This is important because after you manage to get through the while loop once, on the next value of for, that Error(n-1) is still there in the vector and is known to be < Criteria or else the previous iteration would not have ended...