On Jun 11, 2013, at 20:26 , Mimi Celis wrote:
> I am looking at the aov function in R. I see that it uses a modified QR
factorization routine dqrdc2 based on the Linpack routine dqrdc. Pivoting is
done different than the original Linpack function.
>
> My questions:
>
> * Why is it necessary to modify the pivoting strategy? Something
necessary for aov?
> * Will the LAPACK function dgeqp3 work well or would the pivoting have o
be modified?
>
As far as I have understood it, the issue is that to generate the sequential
ANOVA table based on a single QR factorization, you can't have it swapping
terms around, because there are cases where the order of terms matters.
So LAPACK won't do. Or rather, to use it, you'd need to rethink the
algoritm; you may need refactorizing for each line the ANOVA table. It's not
necessarily impossible or seriously inefficient, just one of the things that
nobody seems to have an aching desire to tackle.
-pd
> Thank you
> MRC
>
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>
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