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Re: newbie question: assigment to N-d arrays returns strange values

 From: Amir Seginer Subject: Re: newbie question: assigment to N-d arrays returns strange values Date: Sat, 06 Aug 2005 22:55:44 +0300 User-agent: Mozilla Thunderbird 1.0.6-1.1.fc4 (X11/20050720)

Henry F. Mollet wrote:
If m=zeros(3, 2, 2);
Then what does m(3,:) mean?
I understand m(3,:,:):
octave:14> m(3,:,:)
ans =
ans(:,:,1) =
0  0
ans(:,:,2) =
0  0
Henry

Well, on Matlab, as well as on octave, m(3,:) means a row vector which represents the 2x2 matrix m(3,:,:).

For example, this works on both Ocatve and Matlab

>> m=zeros(3, 2, 2) ;
>> m(3,1,2)=1;
>> m(3,1,1)=1;
>> m(3,2,1)=2;
>> m(3,1,2)=3;
>> m(3,2,2)=4;
>> m
m =

ans(:,:,1) =

0        0
0        0
1        2

ans(:,:,2) =

0        0
0        0
3        4

>> m(3,:)
ans =

1        2        3        4

Since this does work on Octave, I was expecting the assigment

m(3,:) = [1 2 3 4]

to also work (as it does on Matlab).

Thanks,

Amir.

on 8/5/05 11:31 PM, Amir Seginer at address@hidden wrote:

Hello,

This might be a known problem, but I couldn't find any reference to it.
When assigning to an n-dimensional array (see below) I get results which
are different from Matlab. Also, in one case I get some strange values
in the array as well.

I wrote the the following code in Octave (using --traditional):

m=zeros(3, 2, 2) ;
a= [1 2 3 4] ;
m(3, :) = a

m =

ans(:,:,1) =

0        0
0        0
1        2

ans(:,:,2) =

0        0
0        0
0        0

which is not what I expected (3 and 4 were not assigned). Even worse,
when I did

m=zeros(3, 2, 2) ;
a= [ 1; 2; 3; 4] ;
m(3, :) = a

m =

ans(:,:,1) =

0        0
0        0
1        2

ans(:,:,2) =

0.0e+00  *

NaN      NaN
NaN      Inf
NaN      Inf

This gives strange values on the 2nd "page". Further more, in normal
mode the same code gave

octave:8> m=zeros(3, 2, 2) ;
octave:9> a= [ 1; 2; 3; 4] ;
octave:10> m(3, :) = a
m =

ans(:,:,1) =

0  0
0  0
1  2

ans(:,:,2) =

0.0000e+00   5.1715e-319
1.1116e-321    0.0000e+00
0.0000e+00    0.0000e+00

Is there a way to overcome this, or at least get an error/warning. I'm
using octave-2.1.71

Thanks,

Amir.

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