Re: [Caml-list] BigArray.Array2 vs Array.make_matrix

[Xavier Leroy <xavier.leroy@inria.fr>]

> I was wondering what are the relative merits (in terms of speed,
> portability and ease of use) between using arrays of arrays, and the
> BigArray class.
> 
> While web browsing, I saw a couple of people claim that BigArray is
> signigicantly slower than the standard array class:
> 
> http://caml.inria.fr/archives/200105/msg00217.html
>  claims BigArray is 3 times slower
> 
> www.cs.cornell.edu/courses/cs612/2001sp/ projects/ocaml-arrays/OCaml.pd
>  claims BigArray is about 10 times slower

There are earlier discussions of this issue in the archives of the
caml-list.  See for instance my reply:

http://pauillac.inria.fr/bin/wilma_hiliter/caml-list/200207/msg00445.html

In general, bigarrays are slower than regular arrays, although the
slowdown depends a lot on how the code is written, e.g. ensuring that
bigarrays are fully monomorphic improves performance quite a lot.

The main purpose of bigarrays is not to speed up pure Caml code, but
to facilitate interfacing with external numerical libraries.

In some circumstances, bigarrays have a few added bonuses as well:
compact representation of arrays of small floats, small integers, and
complex numbers; support for dimensions >= 2^22 on 32-bit machines;
and no-copying slicing and shrinking operations.  But all this comes
at some expense in speed for raw array accesses.

> Plus an interface to some standard linear algebra code would be nice...

You mean, like LACAML?
  http://www.ai.univie.ac.at/~markus/home/ocaml_sources.html

- Xavier Leroy
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