bugGNU Octave - Bugs: bug #41399, The LU decomposition does not...

 
 

bug #41399: The LU decomposition does not return a lower triangular L

Submitter:  None
Submitted:  Thu 30 Jan 2014 02:37:57 AM UTC
   
 
Category:  Octave Function Severity:  3 - Normal
Priority:  5 - Normal Item Group:  Incorrect Result
Status:  Invalid / Not an Octave Bug Assigned to:  None
Originator Name:  Donald Originator Email:  -email is unavailable-
Open/Closed:  * Closed Release:  * 3.6.4
Operating System:  * Microsoft Windows Fixed Release:  None
Planned Release:  None
* Mandatory Fields

Add a New Comment Rich Markup
   

Thu 30 Jan 2014 06:03:31 AM UTC, comment #1: 

From the docstring for lu:


Compute the LU decomposition of A.  If A is full subroutines from
LAPACK are used and if A is sparse then UMFPACK is used.  The
result is returned in a permuted form, according to the optional
return value P.

[...]

With two output arguments, returns the permuted forms of the upper
and lower triangular matrices, such that 'A = L * U'.  With one
output argument Y, then the matrix returned by the LAPACK routines
is returned.


This behavior is required for compatibility with Matlab.


John W. Eaton <jwe>
Group administrator
Thu 30 Jan 2014 02:37:57 AM UTC, original submission:  


N=10; A=eye(N)+diag(1:(N-1),1) + diag(1:(N-1),-1);
[L,U]=lu(A);
min(diag(L,0)) --> returns zero???
diag(L,3) --> returns -0.5???
sum(~~L(2,:))--> return 9???, row at index=2 is almost full???
max(max(abs(A-L*U))) --> returns 4.9960e-016 as it should be.


Anonymous

 

(Note: upload size limit is set to 16384 kB, after insertion of the required escape characters.)

Attach Files:
   
   
Comment:
   

No files currently attached

 

Depends on the following items: None found

Items that depend on this one: None found

 

Carbon-Copy List
  • -email is unavailable- added by jwe (Posted a comment)
  • -email is unavailable- added by None (Submitted the item)
  •  

    There are 0 votes so far. Votes easily highlight which items people would like to see resolved in priority, independently of the priority of the item set by tracker managers.

    Only group members can vote.

     

    Follow 2 latest changes.

    Date Changed by Updated Field Previous Value => Replaced by
    2014-01-30 jwe StatusNone Invalid / Not an Octave Bug
        Open/ClosedOpen Closed

    Back to the top

    Powered by Savane 3.13-d3ae.
    Corresponding source code