From bug-octave-request at bevo dot che dot wisc dot edu Wed Dec 18 07:52:57 2002
Subject: RE: 0*NaN within matrix multiplication
From: "Lippert, Ross A." <Ross dot Lippert at celera dot com>
To: "John W. Eaton" <jwe at bevo dot che dot wisc dot edu>
Cc: "Paul Kienzle" <pkienzle at jazz dot ncnr dot nist dot gov>,    "Schloegl Alois" <alois.schloegl@tugraz.at>, <bug-octave@bevo.che.wisc.edu>
Date: Wed, 18 Dec 2002 08:52:44 -0500


Does anyone think it is a bad enough bug to want to have
some sort of coding around this?

-r

-----Original Message-----
From: John W. Eaton [mailto:jwe at bevo dot che dot wisc dot edu]
Sent: Tuesday, December 17, 2002 7:40 PM
To: Lippert, Ross A.
Cc: Paul Kienzle; Schloegl Alois; bug-octave at bevo dot che dot wisc dot edu
Subject: RE: 0*NaN within matrix multiplication


On 10-Dec-2002, Lippert, Ross A. <Ross dot Lippert at celera dot com> wrote:

| Ahh.  In that case the bug is smaller (and cuter):
| octave:17> [nan]*[0]
| ans = NaN
| octave:18> [nan nan]*[0;0]
| ans = 0
| 
| Yes, I agree that the above is a bad thing(tm).

This is what you get with the reference implementation of DGEMM (it
has some logic to avoid the multiplication if one of the operands is
zero), but not with the ATLAS implementation (it may also avoid
multiplication by zero, but apparently not if the other operand is NaN
or Inf):

  octave:1> [nan nan]*[0;0]
  ans = NaN
  octave:2> [inf inf]*[0;0]
  ans = NaN

  $ ldd `type -p octave`
    liboctinterp.so => /usr/lib/octave-2.1.40/liboctinterp.so (0x40014000)
    liboctave.so => /usr/lib/octave-2.1.40/liboctave.so (0x40431000)
    libcruft.so => /usr/lib/octave-2.1.40/libcruft.so (0x40640000)
    liblapack.so.2 => /usr/lib/atlas/liblapack.so.2 (0x406a0000)
    libblas.so.2 => /usr/lib/atlas/libblas.so.2 (0x40bcd000)
    libfftw.so.2 => /usr/lib/libfftw.so.2 (0x40e6b000)
    libreadline.so.4 => /lib/libreadline.so.4 (0x40e9f000)
    libncurses.so.5 => /lib/libncurses.so.5 (0x40ec9000)
    libdl.so.2 => /lib/libdl.so.2 (0x40f07000)
    libm.so.6 => /lib/libm.so.6 (0x40f0a000)
    libstdc++-libc6.2-2.so.3 => /usr/lib/libstdc++-libc6.2-2.so.3 (0x40f2b000)
    libc.so.6 => /lib/libc.so.6 (0x40f74000)
    /lib/ld-linux.so.2 => /lib/ld-linux.so.2 (0x40000000)

I don't know what the various vendor versions of the blas do.

jwe



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