# 0-extent matrices?

**Martin Maechler
**
Martin Maechler <maechler@stat.math.ethz.ch>

*Sat, 11 Apr 1998 10:56:16 +0200*

>>>>>* "TL" == Thomas Lumley <thomas@biostat.washington.edu> writes:
*
TL> Is there a good reason not to allow matrix extents to be zero?
No, I don't think so.
And I agree that it would be really useful to have them in circumstances
like yours.
TL> I have been writing a function which fits glms under certain linear
TL> constraints. I fit the model with a reduced set of variables and
TL> then transform back to the original set. This involves operating
TL> on submatrices of the covariance matrix and subsets of the
TL> coefficients. Sometimes these subsets are empty. A zero-length
TL> subset of the coefficient vector causes no problems, but a 0x6
TL> submatrix of the covariance matrix won't work with rbind and cbind.
TL> There appears to be no difficulty in deciding how standard matrix
TL> and array operations should work with a 0x6 matrix and in fact you
TL> might expect that the same C code would usually work.
Could you look into implementing them?
Martin
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