On Wednesday, 21.03.2007 at 09:29 +0000, Prof Brian Ripley wrote: > >OK, I understand the problem now. I was wondering if it something along > >those lines, but initially dismissed that as a possibility since I > >expected 'choose' to be an integer calculation. > > It is not, because it would be far too easy to get integer overflow.
Yes, of course. And, also, as I have now remembered, it is perfectly feasible to use non-integer parameters to n-choose-k as well. It is clearly too long since I did my Stats degrees *blush* > >However, the underlying problem that gave rise to the difficulty was as > >follows. A colleague wishes to create a matrix, where one of the > >dimensions of the matrix is the result of the 'choose' function, i.e. > > > > mycols<-choose(11,6) > > a_matrix<-matrix(0,nrow=11,ncol=mycols) > > > >Clearly, 'ncol' casts mycols as as integer. In this case, a_matrix has > >only 461 columns, not 462. > > > >What's the best way to make this work as required? > > Use round(mycols). I think we ought to do this internally: we do when > using computations via beta/gamma functions. *nods* - thanks. Dave. -- Dave Ewart [EMAIL PROTECTED] Computing Manager, Cancer Epidemiology Unit Cancer Research UK / Oxford University PGP: CC70 1883 BD92 E665 B840 118B 6E94 2CFD 694D E370 Get key from http://www.ceu.ox.ac.uk/~davee/davee-ceu-ox-ac-uk.asc N 51.7518, W 1.2016
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