From koffice-devel  Thu Aug 21 16:48:46 2008
From: Stefan Nikolaus <stefan.nikolaus () kdemail ! net>
Date: Thu, 21 Aug 2008 16:48:46 +0000
To: koffice-devel
Subject: Re: porting to eigen2
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=
=20
around. If it would just store plain doubles, I would agree with you, but i=
t=20
does not.
Some trivial matrix functions should also work with other types and should =
not=20
assume real values as elements, e.g. TRANSPOSE should simply exchange rows =
and=20
columns and leave strings untouched. It's not appropriate to use Eigen in t=
his=20
case. For MUNIT it's not necessary; it's even slower than directly filling =
the=20
ValueArray due to the two conversions made.


Stefan Nikolaus


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