How to vectorize this simple for-loop

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Felix Lauwaert 2015-8-19

评论： Felix Lauwaert 2015-8-19

Hello,

I'm trying to vectorize something like this:

    z=zeros(3); x=[1 2 3]; y=x;
    for i=1:length(x)  %or y, doesn't matter
    z( x(i),y(i) )=z( x(i),y(i) ) + 1;
    end

z= [1 0 0 ; 0 1 0 ; 0 0 1]

What I really want is to do it for any x and y vectors in a 1000by1000 zero matrix.

I tried to do:

z(x,y)=z(x,y)+1;

But I get all values of z =1. I also tried:

z(x.,y.)=z(x.,y.)+1;

But an error message appears.

Thanks for your help.

Matt J 2015-8-19

编辑：Matt J 2015-8-19

   idx=sub2ind(size(z),x,y);
   z(idx)=z(idx)+1;

Felix Lauwaert 2015-8-19

Error using sub2ind (line 52) Out of range subscript.

Felix Lauwaert 2015-8-19

idx=sub2ind([length(x),length(x)],x,y); z(idx)=z(idx)+1;

Is working. Thanks!

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