anti diagonal matrix in mata?

[Gbenga Adejafe]

Is there a function that creates anti diagonal matrix from some vector, something like reverse diag() ?

[Christophe Kolodziejczyk]

If it exists I have not been able to find one. But you could make one yourself by using a permutation vector.

------------------------------------------------- mata (type end to exit) ------------------------------------------
: 
: real matrix antiDiag(real colvector v)
> {
> 
>                 real colvector p
>                 
>                 p = 1::rows(v)
>                 _sort(p,-1)
>                 
>                 return(diag(v)[,p'])
> 
> }

: 
: antiDiag(1::10)
         1    2    3    4    5    6    7    8    9   10
     +---------------------------------------------------+
   1 |   0    0    0    0    0    0    0    0    0    1  |
   2 |   0    0    0    0    0    0    0    0    2    0  |
   3 |   0    0    0    0    0    0    0    3    0    0  |
   4 |   0    0    0    0    0    0    4    0    0    0  |
   5 |   0    0    0    0    0    5    0    0    0    0  |
   6 |   0    0    0    0    6    0    0    0    0    0  |
   7 |   0    0    0    7    0    0    0    0    0    0  |
   8 |   0    0    8    0    0    0    0    0    0    0  |
   9 |   0    9    0    0    0    0    0    0    0    0  |
  10 |  10    0    0    0    0    0    0    0    0    0  |
     +---------------------------------------------------+

: 
: end
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