CODEWITHSUNDEEP
matlab
user1157751
user1157751

Reputation: 2457

Matlab - Integer Comparison Error

I'm trying to compare integers in a while loop, shown below:

Sigma_Wanted_Start = 0.000;
Sigma_Wanted_End   = 0.009;
Sigma_Increment    = 0.001;
Sigma_Current      = 0.000;

while (Sigma_Wanted_End ~= Sigma_Current)
    Sigma_Current = Sigma_Current + Sigma_Increment;
end

If Sigma_Wanted_End == 0.009, then we would stop the for loop. The problem is that the statement is shown true even if Sigma_Wanted_End == Sigma_Current.

Another strange thing is that if Sigma_Wanted_End == 0.008, then the while loop would stop.

I thought it's the difference between integers, and double, so I used double on all the numbers, but the problem still occurred.

Does anybody know why?

Thanks in advance

Upvotes: 0

Views: 118

Answers (2)

Alyafey
Alyafey

Reputation: 1453

floating point representations in matlab are not equal because of rounding problems.

let say if we have 

x = 0.3
 0.4-0.1
 x==y

this will give you false so you could do this

Sigma_Wanted_Start = 0.000;
Sigma_Wanted_End = 0.009;
Sigma_Increment = 0.001;
Sigma_Current = 0.000;
while (~((Sigma_Wanted_End - Sigma_Current)<0.0))
    Sigma_Current = Sigma_Current + Sigma_Increment;
end

Upvotes: 1

Paul R
Paul R

Reputation: 212959

You should not test for exact equality when comparing floating point values, due to the finite precision available. Instead do something like this:

while (Sigma_Current < Sigma_Wanted_End)
    Sigma_Current = Sigma_Current + Sigma_Increment;
end

Upvotes: 2

Related Questions