[Octave-bug-tracker] [bug #48686] Copy of columns of the matrix

[anonymous]

URL:
  <http://savannah.gnu.org/bugs/?48686>

                 Summary: Copy of columns of the matrix
                 Project: GNU Octave
            Submitted by: None
            Submitted on: Wed 03 Aug 2016 10:38:26 AM UTC
                Category: Performance
                Severity: 3 - Normal
                Priority: 5 - Normal
              Item Group: None
                  Status: None
             Assigned to: None
         Originator Name: Polina
        Originator Email: address@hidden
             Open/Closed: Open
         Discussion Lock: Any
                 Release: 4.0.3
        Operating System: Microsoft Windows

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Details:

Dear Developers!

Thank you for your work on Octave! It's really useful soft for me nowdays.

I noticed a problem and decided to report hoping that this could improve
Octave even more.

It seems that implementation of column copy in matrices has some leakage. When
I try to copy columns like

T(:, i+1) = T(:, i);

it takes increadibly long time for the whole matrix.
For my programming I wanted to optimize code like

T(:, i+1) = T(:, i) + v * T(:, i);

for the case when v = 0.
In the end that did slowed my code instead.

I attach a simple test.
It takes 6 minutes for copying of the columns (flag = 0) and less than one
second for analogos copy with addition of 0 * column.

P.S. I tested both with Octave for WIndows and with Octave installed in CygWin
environment.
P.P.S. I tested the same on copying of rows and it seems to be fine.

Kind regards,
Polina



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File Attachments:


-------------------------------------------------------
Date: Wed 03 Aug 2016 10:38:26 AM UTC  Name: test_matrix_copy.m  Size: 464B  
By: None

<http://savannah.gnu.org/bugs/download.php?file_id=38084>

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