From help-request at octave dot org Tue Apr 19 04:20:56 2005
Subject: Re: Easy about Matrices
From: "Peter Bodin" <pbodin at kth dot se>
To: help at octave dot org
Date: Tue, 19 Apr 2005 11:17:21 +0200 (CEST)

> Frank Palazzolo wrote:
>
>>This syntax works as well:
>>
>>x = randn(1,1000);
>>x_positive = (x>=0);
>>x_negative = (x<0);
>>
>>I'm not sure if it's any more efficient, but it seems it would be,
>> since it
>>never needs to build an explicit index vector.
>>
>>-Frank
>>
>>
> This is definitely faster, but it doesn't return the same matrix:
>
> octave:1> x=randn(1,10);
> octave:1> (x>0)
> ans =
>
>  Columns 1 through 8:
>         1        1        0        0        0        0        1
>   0
>  Columns 9 and 10:
>         1        1
>
> octave:3> x(find(x>0))
> ans =
>
>   0.93970  0.38451  0.30387  0.81479  2.46831
>
>
>
>
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>

Hi!

Why not use logical indexing?

x(x>0)

or am I missing the obvoius here?

/PB






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