[Octave-bug-tracker] [bug #42314] Matrix transpose multiply trick - performance bug?

[Ceral Paquet]

URL:
  <http://savannah.gnu.org/bugs/?42314>

                 Summary: Matrix transpose multiply trick - performance bug?
                 Project: GNU Octave
            Submitted by: octavebugs
            Submitted on: Wed 07 May 2014 08:59:30 PM GMT
                Category: None
                Severity: 3 - Normal
                Priority: 5 - Normal
              Item Group: None
                  Status: None
             Assigned to: None
         Originator Name: 
        Originator Email: 
             Open/Closed: Open
         Discussion Lock: Any
                 Release: 3.8.1
        Operating System: GNU/Linux

    _______________________________________________________

Details:

This used to be an issue on MATLAB - see below.

>> A=randn(4000,3000);
>> b=randn(4000,1);
>> tic; q=A'*b; toc
Elapsed time is 0.697953 seconds.
>> tic; qq=(b'*A)'; toc
Elapsed time is 0.0830581 seconds.
>> norm(q-qq)
ans =    7.6550e-12

Is it a bug? I don't know. But it was fixed in MATLAB to make both equally
fast.




    _______________________________________________________

Reply to this item at:

  <http://savannah.gnu.org/bugs/?42314>

_______________________________________________
  Message sent via/by Savannah
  http://savannah.gnu.org/