Re: how to define a function handle in oct-files

[Muthiah Annamalai]

Evan wrote:
> On Jan 10, 2008 9:24 PM, Evan <address@hidden> wrote:
>   
> > I want to define a function like the following in an oct-file
> >
> > function y=fun(f)
> >   g=@(x) 1./f(x);
> >   y=quad(g, 0, 1);
> > endfunction
> >
> > what should I write for the sentence "g=@(x) 1./f(x);"?
> > thanks in advance
> >
> >     
>
> I still don't know if there is any standard method to do this, but
> after look through the head files of Octave, I figure out a way as
> follows
>
>       octave_value_list f = feval("func2str", args(0), 1);
>       std::string fcn = f(0).string_value ();
>       std::string newfcn = "@(x) 1./( (" + fcn + ")(x))";
>       int status;
>       octave_value_list nf = eval_string (newfcn, true, status, 1);
>
>   
This is self-defeating, as I think you must use the Delauny
by invoking Fortran, as otherwise you will not gain much
speed by doing this in an OCT file.
> in "parse.h"
>      extern OCTINTERP_API octave_value_list
>      eval_string (const std::string&, bool silent, int& parse_status,
> int hargout);
> I think "hargout" is a typo for "nargout". I wonder what is
> "parse_status" for. It seems that it is always zero whether the string
> is evaluated successfully or not.
>
>   
Parse status is to return success (0) or failure of parsing the string.
> ps. When trying these things, I encounter another thing I don't understand i.e.
>
> octave:1> @(x) 1./( (@(y) 1./y) (x) )
> ans =
>
> @(x) 1 ./ ((@(y) 1 ./ y;
> ) (x))
>
> octave:2> func2str(  @(x) 1./( (@(y) 1./y) (x) )  )
> ans = @(x) 1 ./ ((@(y) 1 ./ y;
> ) (x))
> octave:3>
>
> Why there are semicolons in the output?
>   
Nothing wrong however!
-Muthu