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## Re: Easy about Matrices

**From**: |
Mike Miller |

**Subject**: |
Re: Easy about Matrices |

**Date**: |
Mon, 18 Apr 2005 18:55:38 -0500 (CDT) |

On Mon, 18 Apr 2005, Quentin Spencer wrote:

`I'm not completely sure if this is what you're looking for, but maybe
``this example helps:
`
x = randn(1,1000);
x_positive = x(find(x>=0));
x_negative = x(find(x<0));

`That seems like it must have been an excellent answer for Alvaro. I have
``a related question. Suppose I have a vector like this:
`
X=[1, 3, 9, 2, 4, 2, 7, 5, 3, 2, 9, 7]';

`And suppose I want the indices of all elements of X that are in this
``vector Y:
`
Y=[2, 3, 9]';
I can see how to do it with a loop...
index=find(X==Y(1)); for i=2:length(Y), index=[index ; find(X==Y(i))]; end

`...but can it be done without a loop? (Also, my method is a little
``awkward and I wouldn't mind hearing about how I could do it better.)
`
Mike
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**Easy about Matrices**, *Alvaro Aguilera*, `2005/04/18`
**Re: Easy about Matrices**, *Quentin Spencer*, `2005/04/18`
**RE: Easy about Matrices**, *Frank Palazzolo*, `2005/04/18`
**Re: Easy about Matrices**, *avraham*, `2005/04/18`
**Re: Easy about Matrices**,
*Mike Miller* **<=**
**Re: Easy about Matrices**, *Geordie McBain*, `2005/04/18`
**Re: Easy about Matrices**, *Mike Miller*, `2005/04/18`
**Re: Easy about Matrices**, *Alvaro Aguilera*, `2005/04/19`
**Re: Easy about Matrices**, *Peter Bodin*, `2005/04/19`
**Re: Easy about Matrices**, *Alvaro Aguilera*, `2005/04/19`
**Re: Easy about Matrices**, *Peter Bodin*, `2005/04/19`
**Re: Easy about Matrices**, *Mike Miller*, `2005/04/19`