[R] Help to make a specific matrix

[Gabor Grothendieck]

On 7/9/05, Jose Claudio Faria <joseclaudio.faria at terra.com.br> wrote:
> Dear R users,
> 
> The solution is probably simple but I need someone to point me to it.
> How can I to generate a matrix from a numeric sequence of 1:10 like 'A' or 'B'
> below:
> 
> A)
> |--------------------|
> |      1  2  3  4  5 |
> |--------------------|
> | 1 |  0             |
> | 2 |  1  0          |
> | 3 |  2  5  0       |
> | 4 |  3  6  8  0    |
> | 5 |  4  7  9 10  0 |
> |--------------------|
> 
> B)
> |--------------------|
> |      1  2  3  4  5 |
> |--------------------|
> | 1 |  0  1  2  3  4 |
> | 2 |  1  0  5  6  7 |
> | 3 |  2  5  0  8  9 |
> | 4 |  3  6  8  0 10 |
> | 5 |  4  7  9 10  0 |
> |--------------------|
> 

Try this and see ?lower.tri

A <- matrix(0,5,5)
A[lower.tri(A)] <- 1:10
B <- A + t(A)