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Subject: Re: [boost] (Boost) QVM update
From: Shakti Misra (shakti.misra.study_at_[hidden])
Date: 2013-01-09 08:22:14

Hi Emil,
I also am waiting to try it out. My environment doesn't allow me to use
boost completely.
I may be getting little greedy, but any chance of using vectorization? :)

On Wed, Jan 9, 2013 at 11:30 AM, Nathan Crookston <
nathan.crookston_at_[hidden]> wrote:

> Hi Emil,
> Emil Dotchevski wrote:
> > Boost QVM has been updated. Note, this library has not been reviewed
> > yet and it is not part of Boost.
> >
> > Comments and bug reports are appreciated.
> >
> I've been looking forward to this library. I often need something like
> this in my work (mixture of graphics programming, image processing, and
> geospatial applications). I wasn't happy with what ublas offered in the
> static-sized 3-8 dimensions, so I rolled my own -- I'd be much happier to
> have something like this, though.
> The documentation seem especially complete. A few questions and comments
> that occurred to me as I was reading through (and occasionally glancing at
> the code):
> * I'm sure [qvms]_traits is used all over the place, but I'd still rather
> see scalar_traits, vector_traits, etc., especially as those may be
> specialized by the user.
> * I thought s_traits was hard to find in the 'Generic programming
> utilities' section. Should it be in the 'Type traits' section instead?
> * It looks like matrix types (probably vectors and quaternions too) must be
> default constructible (for both make and the template conversion operator
> of mat), though I didn't see that particular requirement noted -- am I
> mistaken?
> * The SFINAE page seems to reference itself:
> sfinae
> The boost::qvm::sfinae namespace contains only function names that use
> SFINAE <circular link>. The boost::qvm namespace contains all Boost QVM
> type and function names.
> I would have expected it to link to an explanation of sfinae -- not
> necessarily part of QVM's docs.
> * inverse: I was surprised to see that you're inverting using the matrix
> of cofactors. For my personal education, why do you use that method -- is
> it more stable or efficient than others? A home-rolled implementation I
> did something like the following:
> //Solving Ax = b
> matrix<float> A;
> vector<float> b;
> inverse_matrix<float> inverse_m = invert(m);//actually perform lu
> decomposition
> vector<float> x = inverse_m * b;//actually back-substitutes from lu matrix.
> In that case, I knew that I'd only ever multiply by a vector -- which
> allowed me to use a method which is at least as efficient as matrix
> inversion and more numerically stable. I'm not sure if an inverse_matrix
> type would allow something like:
> matrix<float> A = ...;
> inverse_matrix<float> B = ...;
> auto C = A * B;
> auto D = B * A;
> to be computed as efficiently as if B were really just a matrix type. I
> could look that up tomorrow, when I have a reference on the material. If
> it is, I think it would be interesting to have inverse return a view_proxy.
> * I haven't looked, but I assume QVM is targeting cases where both matrices
> fit into cache? Meaning, it doesn't worry about things like cache
> blocking?
> * I think the swizzling code is interesting. The Accessing * Elements
> pages aren't too informative, though. It would help me if those pages, in
> the 'See also:' section, were to link to examples of their usage.
> * Further on swizzling -- when I'm dealing with OpenGL texture coordinates,
> the canonical names for them are s, t, r and q. Is there an interface
> whereby I could allow writing something like this?
> TexCoord tc1(1, 2, 0, .5);
> TexCoord tc2 = tc1 % TSRQ;
> I don't know that I'll ever need such a thing -- this is mostly out of
> curiosity.
> I haven't had a chance to try QVM out -- I'd like to work up examples with
> e.g., std::array<float,4>, then something with boost::units types as the
> scalar types. In fact, working with the latter would be a killer feature
> from this library for me. I'll let you know what I find.
> Thanks again for making this library available!
> Nate
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