[R] triangular matrix

[Setzer.Woodrow@epamail.epa.gov]

Try this:
> n <- 3
> a <- 2
> out <- diag(n+1)
> out[lower.tri(out)] <-
a^apply(matrix(1:n,ncol=1),1,function(x)c(rep(0,x),1:(n-x+1)))[lower.tri(out)]
> out
     [,1] [,2] [,3] [,4]
[1,]    1    0    0    0
[2,]    2    1    0    0
[3,]    4    2    1    0
[4,]    8    4    2    1

R. Woodrow Setzer, Jr.                                            Phone: (919)
541-0128
Experimental Toxicology Division                       Fax:  (919) 541-5394
Pharmacokinetics Branch
NHEERL MD-55; US EPA; RTP, NC 27711


|--------+----------------------->
|        |          cafa at cin.ufpe|
|        |          .br          |
|        |                       |
|        |          11/01/2000   |
|        |          09:41 AM     |
|        |                       |
|--------+----------------------->
  >--------------------------------------------------------------------------|
  |                                                                          |
  |       To:     r-help at stat.math.ethz.ch, cafa at cin.ufpe.br                 |
  |       cc:                                                                |
  |       Subject:     [R] triangular matrix                                 |
  >--------------------------------------------------------------------------|




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How I make the below matrix

| a^0     0    0    ...  0   |
| a^1     a^0  0    ...  0   |
| a^2     a^1  a^0  ...  0   |
|    .                  |
|    .                  |
|    .                  |
| a^n     a^(n-1) a^(n-2) ... a^0 |

with no loops, where "a" is a constant?

========================================================================
C?zar de Freitas
Depto. de Estat?stica - UFPE
Recife - Pernambuco - Brasil

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