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List:       koffice-devel
Subject:    Re: porting to eigen2
From:       Stefan Nikolaus <stefan.nikolaus () kdemail ! net>
Date:       2008-08-21 16:48:46
Message-ID: 200808211848.46516.stefan.nikolaus () kdemail ! net
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Hi Benoit,

> since eigen2 is now in kdesupport I'm going to port existing eigen1-using
> code to it. I would like to have your confirmation that it is still time to
> port KOffice code (as you're now in soft freeze -- but porting to eigen2
> isn't adding features). Cyrille agreed to that a few weeks ago, but that
> was a few weeks ago so I'd like your blessing again...
>
> A second thing is that I remember that in KSpread we couldn't use eigen1 to
> actually store the matrices as eigen1 was restricted to square matrices. So
> the code looked like
>
> if(matrix is square)
> {
>         create eigen1 matrix from it (copy)
>         use eigen1 to make computations on it
> }
>
> Now eigen2 handles non-square matrices so it could be used right away for
> storage, removing the need to make copies. I don't remember if this would
> be a trivial change or not; in case it is, do you agree that I do it?

I don't think, that that was the reason for not using Eigen as storage.
The class Value is a union of several data types with some conversion logic 
around. If it would just store plain doubles, I would agree with you, but it 
does not.
Some trivial matrix functions should also work with other types and should not 
assume real values as elements, e.g. TRANSPOSE should simply exchange rows and 
columns and leave strings untouched. It's not appropriate to use Eigen in this 
case. For MUNIT it's not necessary; it's even slower than directly filling the 
ValueArray due to the two conversions made.


Stefan Nikolaus


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