how to check convergence

I want to stop this while loop if the means array does not change anymore, so basically when convergence occurs.

while i <= maxIterations
    k = size(seedMeans,1);
    means = UpdateMeans(A,k, clusters);
    i = i+1;

How should I do this?

Answer 1

[KSSV]

YOu have to proceed something like this:

means0 = 0 ;
while i <= maxIterations
    k = size(seedMeans,1);
    means = UpdateMeans(A,k, clusters);
    dm = means0-means ;
    means0 = means ;
    if abs(dm)<=10^-3
        break
    end
    i = i+1;
end

[Dion Liu]

dm = means0-means ;
      means0 = means ;
      if abs(dm)<=10^-3

Can you explain what this part does please?

[KSSV]

means0 is previous iteration value, mean is present iteration value. If both the values are same, the difference dm will be zero. So, it exits from the loop.

[Dion Liu]

so how come you did

abs(dm)<=10^-3

instead of

abs(dm)==0

[KSSV]

It is suggested to use abs(dm)<=10^-3, for comparing floating numbers.

[Walter Roberson]

You could use a tighter tolerance: it just isn't a good idea to check for bit-for-bit equality.

http://matlab.wikia.com/wiki/FAQ#Why_is_0.3_-_0.2_-_0.1_.28or_similar.29_not_equal_to_zero.3F

[Dion Liu]

all right thanks so much

[KSSV]

Thanks is accepting answer..:)