Hi all,
I've been sending questions to various maths & C++ lists but now I may
have found the right place to go! Here is a copy of a recent post;
I'm very interested on any thoughts.
Please feel free to CC me directly as well.
Thanks,
Michael Hopkins
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I am canvassing opinion on the usefulness (or otherwise) of the STL
‘valarray’ for high-performance numerical work in C++. I’m deciding
whether to move my library of numerical algorithms (linear algebra,
simulation, global optimisation, Bayesian methods) from C to C++, as I
now understand the potential benefits of an OO approach.
However, there do seem to be alternatives (Objective-C, Eiffel, Java?)
and I’ve heard several complaints about C++ as a working tool; possibly
as a reaction against the inevitable pressure to go with the flow that
surrounds a major new language. I am trying to achieve runtime speed
(mainly for BLAS/LAPACK-style algorithms), clarity of code, ANSI/ISO
compatibility across compilers/platforms & ease of extension. I’m
currently working on the Macintosh which limits the development tools
somewhat, but I’m hoping that OS X will open up a whole bunch of new
UNIX-based stuff that will solve that.
As I see it, valarray was designed by BS exactly for this purpose; to
allow aggressive optimisation by compilers in various ways e.g. because
it is guaranteed to be alias-free. In theory, this should make it
potentially faster than ANSI C until the restrict keyword is
implemented, should it not?
However, there does seem to be a body of (informed?) opinion that
valarray is ‘broken’ or at least not working well enough to be worth the
effort. Does anyone here have experience of the runtime speed of a
carefully constructed (i.e. avoiding the C++ efficiency pitfalls)
valarray-based set of BLAS, LAPACK or whatever? If so, are you using
slices, iterators etc and doing it fully STL-style or doing access with
more traditional Fortran-style (i,j) operators.
Compiler writers; are you taking full advantage of valarray? Does it
offer what it suggests?
Numerical methods people; have you compared it (on a level playing
field) with C, Fortran, C++ template-based libraries (Blitz, MTL,
POOMA)?
Thanks in advance for any thoughts or pointers,
Mike
P.S. Please CC any replies to my email.
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