About LU factorization

[Claudio L.]

(06-05-2015 09:00 PM)salvomic Wrote:  something like this?

Code:


EXPORT permMatrix(lst)
// given a permutation list (like {1,3,2}) and the matrix dimension, returns a permutation matrix
BEGIN
local j, k, mat, dimen;
dimen:= length(lst);
mat:= MAKEMAT(0, dimen, dimen);
FOR j FROM 1 TO dimen DO
mat(j,lst(j)):= 1;
END; // for
RETURN mat;
END;

I don't have a Prime but looks correct to me, you can test easily that permMatrix(P)*A will swap the rows in any matrix A to the order you specified in the vector P.
EDIT: I mean correct in the algorithm, I think your function is missing the size as argument?: permMatrix(P,3)
EDIT AGAIN: Nevermind... I was misled by your comment in the code, but you fot the size automatically.