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Re: FIXED (again): INTERP2 problem
From: |
Paul Kienzle |
Subject: |
Re: FIXED (again): INTERP2 problem |
Date: |
Sat, 26 Nov 2005 15:23:55 -0500 |
Consider a matrix, e.g.,
octave> X=toeplitz(1:5)
X =
1 2 3 4 5
2 1 2 3 4
3 2 1 2 3
4 3 2 1 2
5 4 3 2 1
You want to be able to take slices of this matrix, such as the second
row:
octave> X(2,:)
ans =
2 1 2 3 4
or even the second and fourth row:
octave> X([2,4],:)
ans =
2 1 2 3 4
4 3 2 1 2
Maybe you don't want the whole slice, just the third and fifth columns:
octave> X([2,4],[3,5])
ans =
2 4
2 2
That's more or less what you are doing below, asking for forty randomly
selected columns out of forty randomly selected rows. Obviously since
your matrix is only 4x6 there are going to be some repeats, so Octave
dutifully returns them.
- Paul
On Nov 26, 2005, at 1:43 PM, Pierre Baldensperger wrote:
Actually I'm pretty much a beginner with Octave / Matlab. At first, I
didn't
manage to keep the vectorized syntax because expressions like
a(yidx,xidx)
weren't interpreted the way I expected them to be. Actually I expected
them
to return the vector of elements a(yidx(i),xidx(i)) for
i=1:size(xidx), but
something else shows up that I don't really understand. Example:
a = [ 1 2 3 4 5 6 ; 7 8 9 10 11 12 ; 13 14 15 16 17 18 ; 19 20 21 22
23 24 ]
xidx = floor(rand(40,1)*6)+1
yidx = floor(rand(40,1)*4)+1
result = a(yidx,xidx)
size(result)
ans =
40 40
What's this beast? If somebody has a teacher's soul and could explain
to me
what this "something else" is, what this syntax actually does and what
it can
be used for: your clarifications are welcome (RTFM links if applicable
:-)!
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-------------------------------------------------------------
- INTERP2 / GRIDDATA : problems using those functions, Pierre Baldensperger, 2005/11/20
- Re: INTERP2 / GRIDDATA : problems using those functions, Jonathan Stickel, 2005/11/20
- Re: INTERP2 / GRIDDATA : problems using those functions, Pierre Baldensperger, 2005/11/21
- Message not available
- Re: INTERP2 / GRIDDATA : problems using those functions, Pierre Baldensperger, 2005/11/22
- FIXED: INTERP2 problem, Pierre Baldensperger, 2005/11/24
- Re: FIXED: INTERP2 problem, Paul Kienzle, 2005/11/25
- FIXED (again): INTERP2 problem, Pierre Baldensperger, 2005/11/26
- Re: FIXED (again): INTERP2 problem,
Paul Kienzle <=
- Re: FIXED (again): INTERP2 problem, Paul Kienzle, 2005/11/26
- Re: FIXED (again): INTERP2 problem, Pierre Baldensperger, 2005/11/27
- Re: FIXED (again): INTERP2 problem, Paul Kienzle, 2005/11/27