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From <Ben.NASA...@rbs.com>
Subject RE: [math] Do the two vectors in RealVector.outerProduct really have to be the same size?
Date Thu, 12 May 2011 15:14:17 GMT
 
Thanks:

https://issues.apache.org/jira/browse/MATH-574

Ben Nasatyr
RBS Global Banking & Markets
Office: +44 20 7085 2371   

-----Original Message-----
From: Gilles Sadowski [mailto:gilles@harfang.homelinux.org] 
Sent: 12 May 2011 16:02
To: user@commons.apache.org
Subject: Re: [math] Do the two vectors in RealVector.outerProduct really have to be the same
size?

Hello.

> 
>     thanks in advance for your time and apologies if this has been raised before (I searched
and couldn't find it).
> 
>     I recently wrote something like
> 
> RealMatrix M = x.outerProduct(y);
> 
> and found it throwing an exception and failing one of my tests because x and y were different
sizes. Fair enough in one sense as this is the documented behaviour but not what one expects
mathematically (see e.g. http://en.wikipedia.org/wiki/Outer_product).
> 
>     To deal with this I found myself writing the following (extremely ugly) code:
> 
> RealMatrix M = (x.getDimension() == y.getDimension()) ?
> 
>     x.outerProduct(y) :
> 
>     (new Array2DRowRealMatrix(x.getData())).multiply(new Array2DRowRealMatrix(y.getData()).transpose());
> 
>     So I have a few questions:
> 
>  *
> Can the restriction that the two vectors in RealVector.outerProduct have to be the same
size be removed? If so, should I enter a bug report or feature request?

Yes, please.

> [...]

Thank you,
Gilles

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