[R] Shafer's MIX: Query on code

[(Ted Harding)]

Thanks to Fernando Tusell and especially to Brian Ripley for
their work on 'mix', leading to an apparently good package
mow available on CRAN.

Going through the R code for the function prelim.mix, I am
wondering why the following method of calculation is used
at one point:

  umd <- as.integer(round(exp(cumsum(log(d)))))

(d is a vector containing, in effect, the numbers of levels of
the factors in col1, col2, ... of the categorical variables.
Therefore umd is a vector containing the numbers of possible
combinations of factor levels in col1, col1&col2, ... )

But why not do it as

  umd <- as.integer(cumprod(d))

?? [It can't be that this number could go out or range, since
that would be equally true of exp(cumsum(log(d)))) ]

With thanks, and best wishes to all,
Ted.


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E-Mail: (Ted Harding) <Ted.Harding at nessie.mcc.ac.uk>
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Date: 29-Apr-03                                       Time: 15:19:57
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