[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]
Re: something like a modulo function (but not)?
From: |
Stefan van der Walt |
Subject: |
Re: something like a modulo function (but not)? |
Date: |
Wed, 27 Oct 2004 19:42:40 +0200 |
User-agent: |
Mutt/1.5.6+20040722i |
The ind2sub function should do what you want:
octave:7> [x,y] = ind2sub([5 5], [3 5 8 10 13 15 18 20 23 25])
x =
3 5 3 5 3 5 3 5 3 5
y =
1 1 2 2 3 3 4 4 5 5
Regards
Stefan
On Wed, Oct 27, 2004 at 11:15:09AM -0600, E. Joshua Rigler wrote:
> I feel a little silly even asking this question, but since when has that
> stopped me :^)? I have a vector of sequential indices to a 2-D matrix
> that I want to convert to a set of column-wise vector indices. For
> example a particular 5x5 matrix would be fortran indexed as:
>
> mtrx = [ 1 6 11 16 21 ]
> [ 2 7 12 17 22 ]
> [ 3 8 13 18 23 ]
> [ 4 9 14 19 24 ]
> [ 5 10 15 20 25 ]
>
> I extract a subset of this matrix that gives me the following vector of
> indices:
>
> idx1 = [ 3 5 8 10 13 15 18 20 23 25 ]
>
> and wish to convert it to something like:
>
> idx2 = [ 3 5 3 5 3 5 3 5 3 5 ]
>
> The first thing that popped into my head was that I would need to use
> the modulo function in Octave (i.e., idx2=mod(idx1,5)), but of course
> that would give me:
>
> idx2 = [ 3 0 3 0 3 0 3 0 3 0 ]
>
> I guess what I really want is something similar to modulo, except where
> mod(n,I*n)=n, not zero ("I" is an integer). The best solution I could
> come up with on my own is:
>
> octave:44> idx2 = mod(idx1,5)+(mod(idx1,5)==0)*5
> idx2 =
>
> 3 5 3 5 3 5 3 5 3 5
>
> Can anyone out there suggest something a little more elegant that would
> have less impact on a long and already computationally intensive
> iterative function? Am I just being dense?
>
> -EJR
-------------------------------------------------------------
Octave is freely available under the terms of the GNU GPL.
Octave's home on the web: http://www.octave.org
How to fund new projects: http://www.octave.org/funding.html
Subscription information: http://www.octave.org/archive.html
-------------------------------------------------------------