# [R] elegant matrix creation

Robin Hankin r.hankin at noc.soton.ac.uk
Tue Jul 12 13:11:47 CEST 2005

```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

```