From octave-maintainers-request at bevo dot che dot wisc dot edu  Fri Sep  8 07:50:34 2000
Subject: Re: [PATCH] Add min/max tests. (4/4)
From: Paul Kienzle <pkienzle at kienzle dot powernet dot co dot uk>
To: "John W. Eaton" <jwe at bevo dot che dot wisc dot edu>
Cc: ejr at EECS dot Berkeley dot EDU, octave-maintainers@bevo.che.wisc.edu
Date: Fri, 8 Sep 2000 13:51:07 +0100

On Thu, Sep 07, 2000 at 08:53:42PM -0500, John W. Eaton wrote:
> On  8-Sep-2000, Paul Kienzle <pkienzle at kienzle dot powernet dot co dot uk> wrote:
> 
> | To make it completely proper is a bit more work.  You must protect the
> | do_fortran_indexing state.
> 
> For the (relatively common) case where a single matrix index is the
> result of a call to find(), it seems like it would make more sense to
> return a special `indexing object' that could be used on a matrix of
> the same shape as the one passed to find() without having to worry
> about do_fortran_indexing.  Would that make sense, or do you think it
> would also be too restrictive?
> 
> jwe
> 
> 

Actually, in this case I should have coded it without the find() as:

    z = x;
    idx = abs(x) > abs(y);
    z(idx) = y(idx);

which gives the same result 2-3 times faster (at least with 2.1.31).  
Since this will work in almost all cases, it doesn't make sense to
create a data type just for the return from find.  Compatibility with
matlab is more compelling, but you get that just by setting
do_fortran_indexing = 1.  

Note that you still need do_fortran_indexing == 1 to handle the nargin==1
case:

    [z, zi] = min(abs(x));
    [nr, nc] = size(x);
    if (nr == 1 || nc == 1)
      z(zi) = x(zi);
    else
      dfi = do_fortran_indexing;
      unwind_protect
	do_fortran_indexing = 1;
	z = x(zi + [0:nc-1]*nr);
      unwind_protect_cleanup
	do_fortran_indexing = dfi;
      end_unwind_protect
    endif

A counter question: why would you ever want do_fortran_index == 0?

	- Paul