Re: indexing in octfile

[David Bateman]

Brian Blais wrote:

> David Bateman wrote:
>
> > Brian Blais wrote:
> >
> > > what is the equivalent cc code for:
> > >
> > > m(3:6)=5
> > >
> > > or
> > >
> > > m(3:6)=6:8;
> > >
> > > or
> > >
> > > m(3:6)=m(3:6)+6:8;
> >
> >
> >
> > The equivalent to index is "assign" which you'll find in 
> > ov-base-mat.cc. However, I don't see a case where you should use such 
> > an example. Better to write a generic function and do the 
> > indexing/assignment exterior to the function eg
>
>
> Thanks for the response,
>
> I realize that this particular example is not a good use of the 
> octfile indexing, but it is simple enough that I can learn how to do 
> the more complicated example I am actually interested in.
Really, even in more complex cases, the example I showed is the better 
way of going, as it removes all the nasty indexing issues from your 
oct-file. You can also then use tricks like

double *result = m.fortran_vec();

for (int i = 0; i < nel; i++)
  result[i] = ??;

and avoid all the expensive range checking, for maximum speed. If you 
want a example then

DEFUN_DLD(myfun,args, , "")
{
 NDArray m = args(0).array_value();
 NDArray n = args(1).array_value();
 octave_value_list ovl = idx_vector idx (Range (6, 8));
 m.assign(ovl, n);
 return m;
}

and the call "myfun(m,5)" or "myfun(m,6:8)" for example

Still I don't see the point...

D.


--
David Bateman                                address@hidden
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Parc Les Algorithmes, Commune de St Aubin    +33 1 69 35 77 01 (Fax) 
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