From help-request at octave dot org Tue Feb  8 09:38:10 2005
Subject: Re: indexing in octfile
From: David Bateman <David dot Bateman at motorola dot com>
To: Brian Blais <bblais at bryant dot edu>
Cc: help at octave dot org
Date: Tue, 08 Feb 2005 16:40:07 +0100

Brian Blais wrote:

> Hello,
>
> I have a question about doing indexing in an oct file.
>
> If the following cc code:
>
>   Matrix m = args(0).matrix_value();
>   idx_vector idx(Range (3,6));
>   Matrix ret = (Matrix) m.index (idx, 0);
>
> is equivalent to the following octave code:
>
>   ret=m(3:6);
>
> 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

DEFUN_DLD(myfun, args, , " ")
{
   NDArray m = args(0).array_value();
   double d = args(1).double_value();
    int nel = m.numel();
    for (int i = 0; i < nel; i++)
       m(i) += d + i;
   return m;
}

and then do

m(3:6) = myfun(m(3:6),6);

This is much cleaner


D.



-- 
David Bateman                                David dot Bateman at motorola dot com
Motorola Labs - Paris                        +33 1 69 35 48 04 (Ph) 
Parc Les Algorithmes, Commune de St Aubin    +33 1 69 35 77 01 (Fax) 
91193 Gif-Sur-Yvette FRANCE

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