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Re: sum() behaving erratically?
From: |
Bart Vandewoestyne |
Subject: |
Re: sum() behaving erratically? |
Date: |
Thu, 7 Oct 2004 02:58:33 -0500 |
User-agent: |
Mutt/1.3.28i |
on 10/6/04 4:14 PM, address@hidden at address@hidden wrote:
> I'm a bit embarrassed to ask this, but here goes:
>
> If I let a=[1,2;3,4]; and then ask for sum(a), sum(a,1) and sum(a,2), I
> get the answers
>
> 4 6 4 6 3
> 7
>
> respectively. Now I let a=[1,2]; and do the same. I now get
>
> 3 1 2 3
>
> indicating that in the second case sum(a) != sum(a,1), in direct violation
> of the documentation in the manual. Is this supposed to be like this and
> didn't I understand things, or is it a bug? (Octave is 2.1.57.)
For what it's worth, here is how the other leading brand behaves:
>> version
ans =
6.5.0.180913a (R13
>> a=[1,2;3,4];
>> sum(a)
ans =
4 6
>> sum(a,1)
ans =
4 6
>> sum(a,2)
ans =
3
7
and
>> a=[1,2];
>> sum(a)
ans =
3
>> sum(a,1)
ans =
1 2
>> sum(a,2)
ans =
3
So the behaviour is the same as in the other leading brand. I also came across
this 'problem' while doing some implementation work, but actually i think the
behaviour as it is is quite intuitive, since when a is a vector, then saying
sum(a) is just saying that you want the sum of all elements of a. Wether a is
a row or a column vector doesn't matter than.
The best thing to do is if you really have a situation where you're summing
over colums or rows, is *always* put the 1 or 2 as an extra argument of sum to
indictate if you really want to sum over columns or rows.
Regards,
Bart
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