[bug #61094] gsl_linalg_LU_decomp fails to compute LU decomposition for some singular matrix

[Anne Cheylus]

URL:
  <https://savannah.gnu.org/bugs/?61094>

                 Summary: gsl_linalg_LU_decomp fails to compute LU
decomposition for some singular matrix
                 Project: GNU Scientific Library
            Submitted by: anne_cheylus
            Submitted on: mar. 31 août 2021 13:11:11 UTC
                Category: Accuracy problem
                Severity: 3 - Normal
        Operating System: Linux Ubuntu, Mac Os X
                  Status: None
             Assigned to: None
             Open/Closed: Open
                 Release: 2.6 and 2.7
         Discussion Lock: Any

    _______________________________________________________

Details:

Dear GSL devloppers,

the gsl_linalg_LU_decomp gives NaN values for singular matrices with a column
filled with zeros. 

I have attached an example with a singular 3x3 matrix 



  double a_data[] = { 0.0, 0.0, 1.0,
                      0.0, 1.0, 1.0,
                      0.0, 1.0, 2.0 };
  gsl_matrix_view m
    = gsl_matrix_view_array (a_data, 3, 3);



that finds a correct LU decomposition with GSL 2.5 but gives NaN with 2.6 and
2.7


GSL version 2.5
lu[1,:] = 0 0 1
lu[2,:] = 0 1 1
lu[3,:] = 0 1 1
p = 0 1 2



GSL version 2.6
lu[1,:] = 0 0 1
lu[2,:] = nan nan nan
lu[3,:] = nan nan nan
p = 0 1 2



Thank you very much for your attention,

Anne Cheylus







    _______________________________________________________

File Attachments:


-------------------------------------------------------
Date: mar. 31 août 2021 13:11:12 UTC  Name: output_2.5.txt  Size: 92o   By:
anne_cheylus

<http://savannah.gnu.org/bugs/download.php?file_id=51845>
-------------------------------------------------------
Date: mar. 31 août 2021 13:11:12 UTC  Name: output_2.7.txt  Size: 128o   By:
anne_cheylus

<http://savannah.gnu.org/bugs/download.php?file_id=51846>
-------------------------------------------------------
Date: mar. 31 août 2021 13:11:11 UTC  Name: minitestlu.c  Size: 1kio   By:
anne_cheylus

<http://savannah.gnu.org/bugs/download.php?file_id=51843>
-------------------------------------------------------
Date: mar. 31 août 2021 13:11:11 UTC  Name: output_2.6.txt  Size: 116o   By:
anne_cheylus

<http://savannah.gnu.org/bugs/download.php?file_id=51844>

    _______________________________________________________

Reply to this item at:

  <https://savannah.gnu.org/bugs/?61094>

_______________________________________________
  Message posté via Savannah
  https://savannah.gnu.org/