Re: Easy about Matrices

[Mike Miller]

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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