Re: gsl container designs

[Rhys Ulerich <rhys.ulerich@gmail.com>]

> I recall from my benchmarking days that -- depending on compiler --
> there is a small dereferencing penalty for packed matrices (vectors
> packed into dereferencing **..* pointers) compared to doing the offset
> arithmetic via brute force inline or via a macro.
> ......
> I haven't
> run the benchmark recently and don't know how large it currently is.  It
> was never so large that it stopped me from using repacked pointers for
> code clarity..

Mostly unscientific, but worth tossing into the mix:

Using Intel 10.1 compilers on a fairly recent AMD chip, 100,000 iterations
of doing the nested pointers approach is neck-and-neck with index arithmetic
on a 10x10 double matrix.  For the 100x100 case it takes 1.3 times longer
to iterate using the nested pointers.  Work in the inner loop "compute
kernel" is
*= against a constant scalar.  Optimization flags on -O3.  I've seen similar
behavior on recent GNU compilers.

I'm happy to provide the test code if anyone's interested.

- Rhys