while loops

First time posting. Excuse if i do not post correctly. My problem is with a while loop. I created my self a short while loop test just to see how it works. i run it and it does what i want. that is to say increase mx by 1 until it hits 3, and then when sum is equal to summ, it performs a. here is what i wrote.

mx=1;

while mx<3.0 mx=mx+1; sum=mx*2; summ =4; if (sum==summ) break a=2*sum end end

My problem is that when i increase mx by 0.1 matlab does not perform the if statement. I know sum and summ will be equal at some point but matlabd never performs a. Any help? thank you.

Answer 1

[Matt Fig]

Also, you might find Cleve's article interesting.

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mx=1;
tol = 1e-8;

while mx<3.0
    mx=mx+1;
    sum=mx*2;
    summ =4;
    if abs(sum-summ)<tol
        a=2*sum
        break
    end
end

Answer 2

[Walter Roberson]

You will find an explanation at this FAQ

By the way, it is a bad practice to name one of your variables with the name of one of the built-in routines such as "sum". Don't make a habit of it or else it will cause you problems later -- problems that you will stare at and stare at and not see because you "know" what you mean the code to do.

Answer 3

[marvin corado]

sorry i meant to put it like this.

mx=1;

    while mx<3.0
        mx=mx+1;
        sum=mx*2;
        summ =4;
        if (sum==summ)
        break
            a=2*sum
        end
    end

[Walter Roberson]

You can go back and edit your question. Just select your code and click on the "Code {}" button.

Answer 4

[marvin corado]

ok i read it and its helpful. I tried implementing a solution by using

areEssentiallyEqual = abs(a-b) < tol

like they say, but cant seem to get it working where would the fix above be placed ?

Answer 5

[marvin corado]

ok what would establish the tol.. is it something i choose or something that needs to be calculated? thank you

[Matt Fig]

Just like in my example above, tol is something you choose.

[Walter Roberson]

Choosing a tolerance is fine if you know something about the floating point representation of the range of values you are using, but for more general usage the tolerance should usually be based upon eps() of the maximum magnitude of the values you are working with.

Answer 6

[Van]

I think the problem is the positioning. Isn't that the "a=2*sum" should be placed above the break?

    % 
mx=1;
while mx < 3.0 
    mx=mx+1; 
    sum=mx*2; 
    summ =4; 
    if (sum==summ) 
        a = 2*sum 
        break
    end
end

which will result to 8. I hope i answer it correctly.