# [R] Help to make a specific matrix

Jose Claudio Faria joseclaudio.faria at terra.com.br
Sun Jul 10 03:30:35 CEST 2005

```Gabor Grothendieck wrote:
> 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)

Dear Gabor,

Thank you, very much: this soluction is nice!

Best,
--
Jose Claudio Faria
Brasil/Bahia/UESC/DCET