FW: Easy about Matrices

[Frank Palazzolo]

Woops - you're right - sorry, I got my threads confused.  I was still
thinking about the zero-crossings problem. :(

-Frank

-----Original Message-----
From: Quentin Spencer [mailto:address@hidden 
Sent: Monday, April 18, 2005 2:20 PM
To: Frank Palazzolo
Cc: address@hidden
Subject: Re: Easy about Matrices


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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