I'm Trying to run iterations until convergence.

Hello,

So baically I have a problem where I am guessing an initial weight (Wi). and then I have to plug in (Wi) into an Equation that looks like this. W6=Wi*(0.95)*(0.97)*...

Then I want to take the answer for W6 and use it in this equation (Y=W6/Wi). Then take the answer for Y plug it into another equation F=(1-Y)*1.06.

Lastly from there, take all these answers I just found and plug into Wtogw=(25000)/(1-F-0.457).

Now. Whatever answer I get for Wtogw, I want to use that as my new Wi and redo the process unti the answer I get for Wtogw is equal to Wi.

I have posted what I have so far. The whole first part of code is just setting variables which have known values. Please tell me what I am doing wrong/missing for the "while" loop.

Answer 1

[Dana]

Well, you haven't actually told us what the problem you're encountering is, but right away I can see several problems. First, your while loop condition is i<=maxIter, but you haven't defined i anywhere. As a result, MATLAB is using the built-in i, i.e., sqrt(-1). In this case, when checking whether i<=maxIter, MATLAB only considers the real part of i, which is 0, and therefore (i<=maxIter) evaluates to true.

Furthermore, since i isn't changing inside the loop, it will always be the case that i<=maxIter, and therefore your loop will never end.

If you want to do this loop a set number of times, you should use a for loop, not a while:

for i = 1:maxIter
    <stuff>
end

[Cole Zajack]

Hello, Sorry I am a bit new to MATLAB, I don't even need to do a set amount of iterations, I mainly just need help on how to properly set up a loop of any kind until my answer converges.

And yes the problem I encountered was an endless loop.

[Cole Zajack]

I don't really know how the formatting of loops goes, I just tried my best from the things I was able to search on the internet

[Dana]

To check for convergence:

% set a convergence tolerance (best choice depends on the specifics
% of your application; you might have to play with this
tol=1e-6;

noconv=true; % = true if convergence hasn't been obtained yet
j=0; % counter to track # of loop iterations
while noconv
    j=j+1; % advance loop counter
    .
    . % your lines up to and including Wtogw = ...
    .
    
    % if either Wtogw is close to Wi, or we've reached the
    % max # of iterations, set noconv=false so there's no more
    % iterations after this one.
    if abs(Wtogw-Wi) < tol || j == maxIter
        noconv=false;
    end
    
    Wi=Wtogw; % update Wi
end

[Cole Zajack]

Where would I include the MaxIter Variable?

[Dana]

Where you had it before, or really anywhere before the start of the loop.

[Cole Zajack]

Do you know why I am still getting an error for maxIter?

[Dana]

MATLAB interprets the statement i<=maxIter as, "Check whether i is less than or equal to maxIter; return true if it is, return false if it's not."

That's not what you want to do here. Rather, you simply want to define maxIter, just as you did originally:

maxIter = 100;