[Octave-bug-tracker] [bug #60274] GSVD reordering (matlab compatibility)

[Leonardo]

URL:
  <https://savannah.gnu.org/bugs/?60274>

                 Summary: GSVD reordering (matlab compatibility)
                 Project: GNU Octave
            Submitted by: pocker
            Submitted on: Ter 23 Mar 2021 08:21:31 -03
                Category: Octave Function
                Severity: 3 - Normal
                Priority: 5 - Normal
              Item Group: Matlab Compatibility
                  Status: None
             Assigned to: None
         Originator Name: 
        Originator Email: 
             Open/Closed: Open
                 Release: dev
         Discussion Lock: Any
        Operating System: GNU/Linux

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Details:

Hi.

The ordering of the elements in the output of gsvd is in reverse order
compared to Matlab.

After commands

>> A = [1 1 3; 3 1 2; 2 1 1];
>> B = [2 0 1; 2 1 -1;1 0 0];
>> [U, V, X, C, S] = gsvd (A, B); 
>> diag(C)
ans =

0.9968
0.6072
0.3022

while in matlab diag(C) produces 0.3022, 0.6072, 0.9968.

A simple workaround is 

>> C = diag(flipud(diag(C)));
>> S = diag(flipud(diag(S)));
>> U = fliplr(U);
>> V = fliplr(V);
>> X = fliplr(X);

Side note: matrix X has wrong results. See bug #60273.
https://savannah.gnu.org/bugs/?60273

This affects, at least, v. 6.2.0 and 7.0.0 (4a516dce916c+). Both compiled from
source, debian 10. 

Kind regards,
Leonardo




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