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[Octave-bug-tracker] [bug #45890] Sparse A*x and A+B are a bit slow

From: Rik
Subject: [Octave-bug-tracker] [bug #45890] Sparse A*x and A+B are a bit slow
Date: Wed, 15 Aug 2018 12:19:29 -0400 (EDT)
User-agent: Mozilla/5.0 (X11; Ubuntu; Linux x86_64; rv:61.0) Gecko/20100101 Firefox/61.0

Follow-up Comment #11, bug #45890 (project octave):

I extracted the benchmarking code from the original post and have uploaded it
as bm_sparse.m.

Running the CLI with tip df27088c307f I get

GNU Octave Version: 5.0.0 (hg id: hg-id-disabled)
GNU Octave License: GNU General Public License
Operating System: Linux 4.4.0-131-generic #157-Ubuntu SMP Thu Jul 12 15:51:36
UTC 2018 x86_64
Package Name  | Version | Installation directory
          io  |  2.4.11 | /home/rik/.octavepkg/io-2.4.11
  statistics  |   1.4.0 | /home/rik/.octavepkg/statistics-1.4.0

N=1000000 NNZ=20000000 NRUNS=5
 sparse: 3.949250 (0.013439)
 2*A   : 0.233298 (0.006160)
 A'    : 3.075504 (0.006592)
 A+B   : 0.679681 (0.008432)
 A*x   : 0.544324 (0.011615)
 A'*x  : 3.657135 (0.027786)

Since the original issue report was from 2015, could someone try getting
running the script in Matlab to get more up-to-date results?

The only thing that sticks out to me is

 A'*x  : 3.657135 (0.027786)

This looks to be the sum of the transpose operation and the multiply
operation.  When calling BLAS/LAPACK Octave tries to avoid calculating the
transpose itself and instead passes along an appropriate flag to the
underlying library.  Is there something similar that we could do with sparse


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