From sources-request at octave dot org Fri Jul 23 09:59:29 2004
Subject: sub2ind() convenience patch
From: "John W. Eaton" <jwe at bevo dot che dot wisc dot edu>
To: etienne at cs dot uky dot edu
Cc: octave-sources at octave dot org
Date: Thu, 22 Jul 2004 16:45:19 -0400

I applied this patch.

Thanks,

jwe

On 29-May-2004, Etienne Grossmann <etienne at cs dot uky dot edu> wrote:

| 
| 
|   Hi all,
| 
| I propose the following patch so that does not gripe about the size of
| its index arguments, as long as the number of elements is right.
| 
|   With this patch, code to reshape index lists passed to sub2ind()
| becomes unnecessary. Advantage: shorter code.
| 
|   For example,
| 
|     octave:34> sub2ind ([3,4,2],[1 3 2 3],[1 2 4 4],[2 1 2 2])
|     ans =
| 
|     13   6  23  24
| 
|     octave:35> sub2ind ([3,4,2],[1 3 2 3],[1 2 4 4],[2 1 2 2]')
|     error: sub2ind: all index arguments must be the same size
|     error: evaluating if command near line 49, column 6
|     error: evaluating if command near line 42, column 4
|     error: evaluating if command near line 41, column 2
|     error: evaluating for command near line 39, column 7
|     error: evaluating if command near line 33, column 5
|     error: evaluating if command near line 32, column 3
|     error: called from `sub2ind' in file `/usr/share/octave/2.1.57/m/general/sub2ind.m'
|     octave:35> mysub2ind ([3,4,2],[1 3 2 3],[1 2 4 4],[2 1 2 2]')
|     ans =
| 
|     13   6  23  24
| 
|   The overhead seems reasonable or negative (!) (timing of mysub2ind
| is on the right).
| 
| ======================================================================
|      octave:57> T = 100; szs = [3 5 4]; 
|      for N=[5 10 50 100 1000, 10000],
|        N
|        i1 = 1+floor(szs(1)*rand(1,N));
|        i2 = 1+floor(szs(2)*rand(1,N));
|        i3 = 1+floor(szs(3)*rand(1,N)); 
|        tic; 
|        for i = 1:T, 
| 	 sub2ind (szs,i1,i2,i3);
|        end; tt=toc/T; tic; 
|        for i = 1:T,
| 	  mysub2ind (szs,i1,i2,i3); 
|        end; 
|        [tt, toc/T]
|      end
| 
|      N = 5
|      ans =
| 
|        0.0016043  0.0015547
| 
|      N = 10
|      ans =
| 
|        0.0015739  0.0013806
| 
|      N = 50
|      ans =
| 
|        0.0016303  0.0014407
| 
|      N = 100
|      ans =
| 
|        0.0017061  0.0016547
| 
|      N = 1000
|      ans =
| 
|        0.0026176  0.0024954
| 
|      N = 10000
|      ans =
| 
|        0.012621  0.013198
| ====================================================================== 
| 
|   Just my 2c contribution,
| 
|   Etienne 
| 
| 
| ======================================================================
| --- /usr/share/octave/2.1.57/m/general/sub2ind.m        2004-04-11 23:29:44.000000000 -0400
| +++ ./mysub2ind.m       2004-05-29 20:10:50.000000000 -0400
|  at @ -46,9 +46,9 @@
|               error ("sub2ind: index out of range");
|             endif
|           else
| -           if (all (size (first_arg) == size (arg)))
| +           if (prod (size (first_arg)) == prod (size (arg)))
|               if ((i > nd && arg == 1) || (arg > 0 & arg <= dims(i)))
| -               ind += scale(i-1) * (arg - 1);
| +               ind(:) += scale(i-1) * (arg(:) - 1);
|               else
|                 error ("sub2ind: index out of range");
|               endif
| ======================================================================
| -- 
| Etienne Grossmann ------ http://www.cs.uky.edu/~etienne