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Subject: Re: [ublas] Fast small matrices / homogeneous matrices with uBlas
From: Nasos Iliopoulos (nasos_i_at_[hidden])
Date: 2010-08-09 07:20:22
Thomas,
There is an active discussion and a proposal that will bring fixed vector and fixed matrices (appropriate for small containers) into uBlas. My feeling is that it is getting to a good shape and will probably make it into the next release. Follow this post for some code:
http://lists.boost.org/MailArchives/ublas/2010/07/4500.php
> And secondly, it cannot use the matrices structure such as the fact
> that the last line of an homogenous
> matrix never changes.
Although this is the case with some applications (and even some graphics API providers, like AMD), there are applications that fixing the last row is not desirable (i.e. when you do projections and expect to use the w component of your 4 vector prior to perspective division). I suppose uBlas will support fixed containers in the future, but I find unlikely that it will make any assumptions like homogeneity (in which case you just need to divide by the last element, if you mean to retrieve 3D points).
Best
Nasos
> Date: Mon, 9 Aug 2010 11:32:27 +0900
> From: thomas.moulard_at_[hidden]
> To: ublas_at_[hidden]
> CC: fbleibel_at_[hidden]; florent_at_[hidden]
> Subject: [ublas] Fast small matrices / homogeneous matrices with uBlas
>
> Hello everyone,
> I am currently evaluating the possibility for uBlas to have a better
> support for small matrices.
> In particular, 3d transformation matrices represented by homogenous matrices.
>
> First, I have seen that uBlas is slower than libraries specifically
> targeted for small matrices like tvmet.
> And secondly, it cannot use the matrices structure such as the fact
> that the last line of an homogenous
> matrix never changes.
>
> I was wondering if anyone here would have tried to tackle these problems?
>
> Any advice would be greatly appreciated,
> --
> Thomas Moulard
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> Sent to: nasos_i_at_[hidden]