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Re: Calling octave functions from oct-files

From: Evan
Subject: Re: Calling octave functions from oct-files
Date: Thu, 17 Jan 2008 13:21:07 +0800

On Jan 17, 2008 12:16 AM, Przemek Klosowski <address@hidden> wrote:
> I think you may have a wrong impression on why and how to
> speed-optimize in Octave.  The Octave calculation engine is very
> fast---once you have marshalled the arguments, it goes to pretty well
> optimized libraries, and rips through data.  The delays are caused by
> slow interpretation of control structures (for/while loops) and by
> extraneous manipulation of the arguments (extra copies, reallocation, etc).
> When Octave interpreter runs, it scans your scripts and arranges for
> the execution of commands therein, by keeping track of arguments,
> building data structures to pass to the library routines and calling
> them. If you write an .oct file with feval()s you are essentially
> replicating what the interpreter does, so no wonder it is as slow or
> slower than the scripts.
> To speed things up you'd need to rewrite them in C/C++ completely. Of
> course, in the extreme, you could write C/C++ completely independently
> from Octave, but you will probably find useful things in the octave
> library will help you---and it's nice to be able to use your
> computation code from within Octave, for data I/O, plotting, etc.  You
> need to directly call the binary library routines that the Octave
> interpreter uses, It actually is kind-of like your (*p)(args) but you
> do need to get the specific details right.
> THere's a document called 'Da Coda Al Fine' describing writing .oct
> files: . Beyond that,
> there's some info on the web, especially in the archives of this
> mailing list

Thanks for the detailed explanation.

The problem in which I am involved is like this, first I write my
program completely in octave scripts. Then I found it too slowly
because there are loops in a function and these loops cannot be
vectorized. So I want to rewrite the function in oct-file. However, in
the function there is a definition of a function handle. I would have
rewritten this definition in complete C++ code too if I know how.
Because I don't know how to define a function handle from another, I
fall back on feval and eval_string expecting that in oct-files they
would be as fast as in octave scripts, and the loops in oct-file would
be much faster than that in octave script, so I would finally get a
faster oct-file. Unfortunately, the defined function handle is used in
the loops and cause the loops even slower than when it is in octave
scripts (I know this because if I call from the oct-file an octave
script to accomplish the definition of the function handle instead of
using feval and eval_string, the loops would be very fast).

That's why I am seeking methods of defining a function handle in
oct-files without using feval or eval_string.

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