[SciPy-dev] Re: [SciPy-user] Low-level code integration discussion at scipy'03?

Prabhu Ramachandran prabhu at aero.iitm.ernet.in
Wed Sep 3 12:56:59 CDT 2003


>>>>> "FP" == Fernando Perez <fperez at colorado.edu> writes:

[ FP's nice 6d example ]

    FP> That's it.  ONE line of actual code!  A version of this done
    FP> with hand loops requires obviously 7 nested for loops.  Since
    FP> I needed similar code for dimensions 1..6, I wrote
    FP> preprocessor macros to generate all versions from a 'template'
    FP> (meaning, another macro, not a C++ template<>).  This is, of
    FP> course, ugly.

Interesting example but I'd imagine that apart from you and some
string theorists (are there any here?) most of us mere mortals would
deal with 3 to 4 d data. ;-) Agreed a one liner is a lot nicer but 3
nested loops are quite normal.

So indeed blitz does have lots of advantages.  In fact its the fastest
way to get a 3 fold increase over plain Python Numeric.

    FP> Having said that, the above one-liner performs about 3 times
    FP> slower than the loop macro version for d=6.  For d=1 they are
    FP> about even, the blitz one-liner gets worse as d increases.  I
    FP> posted to the blitz list asking about this, but no response so
    FP> far.

Ahh. :)

[snip]

    >> 3. If plain old inlined C code does indeed perform better than
    >>    the
    >> blitz equivalents, it sure would be useful to have the cleaner
    >> API anyway.  Afterall performance is a key issue here.  Having
    >> a cleaner API (without fancy expression templates but without
    >> having to convert between C++ and Python data) would really be
    >> useful in any case.

    FP> This, we agree 100% on.  In fact, if the C API offered a way
    FP> to index high rank arrays without manually computing stride
    FP> offsets on every access, that would probably satisfy a
    FP> significant fraction of usage cases.  I consider one-liners
    FP> like the above icing on the cake, but A(i,j,k) indexing is
    FP> really a significant change which makes development far more
    FP> productive.

Great!  So we have three strong votes on this on this.

cheers,
prabhu




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