[R] matrix exponential: M^0

[Thomas Lumley]

On Tue, 20 Jan 2004, Federico Calboli wrote:

> Dear All,
>
> I would like to ask why the zeroeth power of a matrix gives me a matrix
> of ones rather than the identity matrix:

Because ^ is not the matrix power. It's the elementwise power.

	-thomas


> > D<-rbind(c(0,0,0),c(0,0,0),c(0,0,0))
> > D<-as.matrix(D)
> > D
>      [,1] [,2] [,3]
> [1,]    0    0    0
> [2,]    0    0    0
> [3,]    0    0    0
>
> > D^0
>      [,1] [,2] [,3]
> [1,]    1    1    1
> [2,]    1    1    1
> [3,]    1    1    1
>
> I would have expected the identity matrix here.
>
> I find the same result with every other square matrix I used.
> BTW, I am using R 1.8.1 on Linux Mandrake 9.1
>
> Cheers,
>
> Federico Calboli
> --
>
>
>
> =================================
>
> Federico C. F. Calboli
>
> PLEASE NOTE NEW ADDRESS
>
> Dipartimento di Biologia
> Via Selmi 3
> 40126 Bologna
> Italy
>
> tel (+39) 051 209 4187
> fax (+39) 051 251 208
>
> f.calboli at ucl.ac.uk
>
> ______________________________________________
> R-help at stat.math.ethz.ch mailing list
> https://www.stat.math.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide! http://www.R-project.org/posting-guide.html
>

Thomas Lumley			Assoc. Professor, Biostatistics
tlumley at u.washington.edu	University of Washington, Seattle