David Abrahams said: (by the date of Sun, 18 Jun 2006 15:49:16 -0400)

Janek Kozicki <janek_listy@wp.pl> writes:

...

That something IMHO is a wiki with specifications of those libraries (when decided to decouple dimensions, units and linear algebra (not geometry!)).

Since I'm working on a linear algebra library I've noting with some confusion all the talk of vectors and matrices in the PQS thread. Can someone give me the three-sentence summary that explains why anyone would think to couple linear algebra and units/dimensions in the first place? I mean, can't you just make a vector of velocities or whatever? Or is this about vectors where each element has different dimensions?

Yes, it is just about vectors and matrices where each element has different dimensions. It is useful for certain calculations. Leland Brown gave an example from his own program: http://lists.boost.org/Archives/boost/2006/06/106412.php My apologies for lack of imagination to get a good name. I picked 'linear algebra' just becasue I was sure that 'geometry' (suggested by Andy) is certainly a bad name. But now Geoffrey Irving has now a better idea to call it 'vectors'. Maybe even 'small vectors'. Geoffrey Irving said:

Most people who see linear algebra will think large dimensional spaces, large dimensional linear system solves, eigen-analysis, etc. How about just 'vectors'?

If you want to suggest another name, please go on :) -- Janek Kozicki |

David Abrahams said: (by the date of Sun, 18 Jun 2006 19:10:11 -0400)

I don't think that's an improvement, if you're working with matrices too. Sounds like linear algebra to me.

My library is designed to work with fixed- as well as variable-sized structures, and it should be possible to use fusion to build heterogeneous vectors and matrices compatible with my library, so I hope no extra library will be needed.

Hello David, can we have a sneak peek at your library? I have looked into the vault but couldn't find it. I also would be very happy to help you working on it. I have few concerns here, and would be grateful if you'd answer that: 1. will your library provide functions useful when working with small vectors like: cross product, normalize (scale vector so its length==1), norm (returns squared length), length, etc... ? 2. will your library allow Boost.Quaternions to be extended in a way that those two libraries together will be useful for geometrical rotations? 3. will your library provide a way to solve equation Ax=b (A is matrix, b and x are vectors, and x is the unknown). The background for question 2 above: Author of Boost.Quaternions tried to extend the library with code that would allow geomtetrical rotations, but at that time only Boost.Ublas library was available. After some investigation he discovered that matrices and vectors from ublas are unsuitable for the task, and finally he gave up. Boost.Quaternions would then have following functions added: from_rotation_matrix(matrix<3,3,T>) to_rotation_matrix() from_axis_angle(vector<3,T1> axis, T2 angle) to_axis_angle() to_euler_angles() operator*(vector<3,T1>,quaternion<T2>) and few others. -- Janek Kozicki |