[Octave-bug-tracker] [bug #39834] vertcat() very slow compared to horzcat()

[Rik]

URL:
  <http://savannah.gnu.org/bugs/?39834>

                 Summary: vertcat() very slow compared to horzcat()
                 Project: GNU Octave
            Submitted by: rik5
            Submitted on: Tue 20 Aug 2013 09:18:10 PM PDT
                Category: Octave Function
                Severity: 3 - Normal
                Priority: 5 - Normal
              Item Group: Performance
                  Status: None
             Assigned to: None
         Originator Name: 
        Originator Email: 
             Open/Closed: Open
         Discussion Lock: Any
                 Release: dev
        Operating System: GNU/Linux

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Details:

Running what looks to be equivalent workloads through vertcat and horzcat
produce very different running times---about 9X slower for vertcat.  The code
is attached below as bm_vertcat.m.


N = 1e3;
################################################################################
clear y1;
y1 = zeros (N,N);
x = repmat ({[1:N]}, N, 1);
tic;
y1 = vertcat (x{:});
toc

clear y2;
x = repmat ({[1:N]'}, 1, N);
tic;
y2 = horzcat (x{:});
toc


And when run


Elapsed time is 0.095994 seconds.
Elapsed time is 0.010987 seconds.





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File Attachments:


-------------------------------------------------------
Date: Tue 20 Aug 2013 09:18:10 PM PDT  Name: bm_vertcat.m  Size: 454B   By:
rik5

<http://savannah.gnu.org/bugs/download.php?file_id=28891>

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