Re: [R] elegant matrix creation

From: Arne Henningsen <ahenningsen_at_email.uni-kiel.de>
Date: Tue 12 Jul 2005 - 21:53:06 EST

Maybe not elegant, but I guess this function does what you want:

f <- function( x ) {

   n <- length( x ) + 1
   m <- matrix( 0, nrow = n, ncol = n )
   diag(m) <- 1
   for( j in 1:( n-1 ) ) {

      for( i in ( j+1 ):n ) {
         m[ i, j ] <- prod( x[ j:(i-1) ] )
      }

   }
   return( m )
}

Best wishes,
Arne

On Tuesday 12 July 2005 13:11, Robin Hankin wrote:
> Hi
>
> I want to write a little function that takes a vector of arbitrary
> length "n" and returns a matrix of size n+1 by n+1.
>
> I can't easily describe it, but the following function that works for
> n=3 should convey what I'm trying to do:
>
>
> f <- function(x){
> matrix(c(
> 1 , 0 , 0 , 0,
> x[1] , 1 , 0 , 0,
> x[1]*x[2] , x[2] , 1 , 0,
> x[1]*x[2]*x[3], x[2]*x[3], x[3], 1
> ),
> 4,4, byrow=T)
> }
>
> f(c(10,7,2))
> [,1] [,2] [,3] [,4]
> [1,] 1 0 0 0
> [2,] 10 1 0 0
> [3,] 70 7 1 0
> [4,] 140 14 2 1
>
>
>
> As one goes down column "i", the entries get multiplied by successive
> elements of x, starting with x[i], after the first "1"
>
> As one goes along a row, one takes a product of the tail end of x,
> until the zeroes kick in.
>
>
> Am I missing some clever solution?
>
>
>
> --
> Robin Hankin
> Uncertainty Analyst
> National Oceanography Centre, Southampton
> European Way, Southampton SO14 3ZH, UK
> tel 023-8059-7743
>
> ______________________________________________
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-- 
Arne Henningsen
Department of Agricultural Economics
University of Kiel
Olshausenstr. 40
D-24098 Kiel (Germany)
Tel: +49-431-880 4445
Fax: +49-431-880 1397
ahenningsen@agric-econ.uni-kiel.de
http://www.uni-kiel.de/agrarpol/ahenningsen/

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Received on Tue Jul 12 21:57:04 2005

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