About LU factorization

[salvomic]

(06-05-2015 08:38 PM)Claudio L. Wrote:  To get the permutation matrix, simply create an NxN matrix with all zeros, and for each row, take a number off the list, and put a 1 in the corresponding column.
For example:
[ 1 , 3 , 2 ] --> Put a 1 in the 1st column on row 1, on row 2 put it in the 3rd column, and on the 3rd row put it in the 2nd column.
You'll get [[ 1 0 0 ] [0 0 1] [0 1 0]], which is what you are looking for.

thank you Claudio!

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;