Question about LU decomposition

[forkandwait]

Hi all,

Let A = [2 4; 4 11].

Then the output from the lu command is 

L = [1 0; 1/2 1]
U = [4 11; 0 -3/2]
P = [0 1; 1 0]

This is great... but it is different from what would be generated if the 
permutation hadn't been done first, which would have been

L = [1 0; 2 1]
U = [2 4; 0 3]

This difference wouldn't be a problem, except I am just starting to work 
through Gilbert Strang's "Intro to Applied Mathematics" using the computer as a 
crutch (^H^H learning tool), and Octave's answers don't match the book 
(generally because he doesn't permute the matrices).  (This matrix is on p 20).

I am not sure what my question is exactly, but maybe for starts:

(1) is there a way to run lu() without permuting?

(2) what is the long story on permuting and LU decomposition -- is it wrong to 
not permute?  Is there a relationship between all the possible decompositions?  
etc etc (a link would be awesome...)

Thanks again