Re: Calling octave functions from oct-files

[Carlo de Falco]

Hi,
I am not really sure wether this is of any help,
but you could have a look at the source code of the
ODE/DAE solver functions which all can take function
handles as an input, and then have to evaluate them repeatedly.

for example I see (in src/DLD-FUNCTIONS/daspk.cc) things like

daspk_fcn = c(0).function_value ();     

that might be related to what you want to do.
c.


On 17/gen/08, at 05:21, Evan wrote:

> 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: http://octave.sourceforge.net/coda/index.html . 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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