# wrong number of groups in classification output

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- October 6, 2004 at 4:14 am #393browntMember
Hi!

I am doing non hierarchical classifications and when I specify a certain number of groups, I often (but not always) get one more group than I requested. For example, if I specify that I want 20 groups in the output, I will get 21 groups numbered from 1 to 21. Then if I try for 19 groups or 21 groups, I will get the correct amount of groups! This has been happening in both PATN 3.01 and 3.02. Is this problem fixable? I can’t figure it out!

Cheers,

Tiff.

October 7, 2004 at 9:27 am #451leeKeymasterHi Tiffany

PATN’s convergence to the requested number of groups in non-hierarchical classification can be sensitive to starting conditions. In some cases, the exact number of groups cannot be achieved. This usually means that the requested number sits on an unstable point.

Requesting a different number of groups changes the scenario for the first phase, usually resulting in PATn generating a different suite of seed objects. This condition can certainly result in generating the number of groups you originaly requested.

We use a ‘branch and bound’ algorithm to try and converge on your selected number of groups. This usually ‘works’, but in the real world, there are no guarantees that it will converge to your requested number.

We will however see if we can improve the convergence.

Lee

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