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Re: Easy about Matrices

From: Quentin Spencer
Subject: Re: Easy about Matrices
Date: Mon, 18 Apr 2005 13:20:06 -0500
User-agent: Mozilla Thunderbird 1.0.2-1.3.2 (X11/20050324)

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.

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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