Re: how to create a permutation matrix

[c.]

On 26 Jan 2015, at 18:35, Jordi Gutiérrez Hermoso <address@hidden> wrote:

> On Mon, 2015-01-26 at 17:57 +0100, c. wrote:
>>>> [l, u, p] = lu (a' * a);
>>>> typeinfo (p)
>> ans = permutation matrix
>> 
>> is there a way to create an object of his type in an m-file?
> 
>    
> https://www.gnu.org/software/octave/doc/interpreter/Creating-Permutation-Matrices.html
> 
> HTH,
> - Jordi G. H.

Thanks, 

That was exactly what I was looking for, I knew it was somewhere but I forgot 
where ;)
Is it expected that :

>> P = eye (4);
>> P = P([2 1 3 4], :);
>> typeinfo (P)
ans = permutation matrix

but 

>> P = eye (4);
>> P ([1 2], :) = P([2 1], :);
>> typeinfo (P)
ans = matrix

BTW the reason I was asking is that I was trying to implement this algorithm 
[1] in 
an m-file (see attachment).

Does anyone else need this? If so maybe I could commit it to the linear-algebra 
package?

c.

[1] 
http://www.mcs.anl.gov/petsc/petsc-current/docs/manualpages/Mat/MatReorderForNonzeroDiagonal.html

reorder_for_nonzero_diagonal.m
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