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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