From bug-octave-request at bevo dot che dot wisc dot edu Tue Dec 10 13:28:23 2002
Subject: Re: 0*NaN within matrix multiplication
From: Paul Kienzle <pkienzle at jazz dot ncnr dot nist dot gov>
To: "Lippert, Ross A." <Ross dot Lippert at celera dot com>
Cc: Schloegl Alois <alois dot schloegl at tugraz dot at>, bug-octave@bevo.che.wisc.edu
Date: Tue, 10 Dec 2002 14:27:20 -0500

0 * NaN and NaN * 0 should both be NaN regardless of the precision in the
arithmetic.  Is LAPACK doing some optimization so that it is not calculating
the product when the first operand is zero?

Paul Kienzle
pkienzle at users dot sf dot net


On Tue, Dec 10, 2002 at 02:10:15PM -0500, Lippert, Ross A. wrote:
> 
> Why is this a bug?  Since when did (y*B)' == B'*y' in inexact arithmetic?
> 
> -r
> 
> -----Original Message-----
> From: Schloegl Alois [mailto:alois dot schloegl at tugraz dot at]
> Sent: Tuesday, December 10, 2002 1:39 PM
> To: bug-octave at bevo dot che dot wisc dot edu
> Subject: 0*NaN within matrix multiplication
> 
> 
> octave> x=[-2:2;4:8]';
> octave> y=x;y(2,1)=nan;y(4,2)=nan;
> octave> B=[1,0,2;0,3,1];
> octave> 
> octave> (y*B)'
> ans =
> 
>     -2   NaN     0     1     2
>     12    15    18   NaN    24
>      0   NaN     6   NaN    12
> 
> octave> B'*y'
> ans =
> 
>     -2   NaN     0   NaN     2
>     12   NaN    18   NaN    24
>      0   NaN     6   NaN    12
> 
> 
> The same behaviour is observed in 2.1.40
> Is this a bug or an undocumented feature? 
> 
>  A. 
> 
> 
> 
> 
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Octave is freely available under the terms of the GNU GPL.

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