Herve Stolowy <[email protected]> asks:
> To my knowledge, the cluster commands of Stata perform a
> hierarchical agglomerative clustering.
>
> I would like to perform a hierarchical divisive (or descending)
> clustering. Do you know if there is special command for that in
> Stata?
Stata's -cluster- command does not include any divisive
hierarchical clustering routines. The reason is that for all but
very small datasets (small N) the computational time of divisive
methods is unreasonable.
The "[CL] Cluster Analysis" manual mentions this and points
out that while algomerative methods have a large task of
checking
N(N-1)/2
possible first combinations of observations, divisive methods
have the almost impossible task of checking
2^(N-1) - 1
possible first divisions of the data. For aglomerative methods
the computational burden grows quadratically with N. For
divisive methods it grows exponentially.
The formulas for N above are just for the first aglomeration or
division. Each additional step of clustering follows along
similarly.
Ken Higbee [email protected]
StataCorp 1-800-STATAPC
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