MATLAB: I am trying to create two vectors out of one,x, where one will contain all the positive elements and the other all the negative elements.

loopsvector

%this program creates vectors N and P out of x
%N will contain negative elements and P the positive elements
x=[-3.5 -5 6.2 11 0 8.1 -9 0 3 -1 3 2.5];
for k=length(x);
    if x>=0
        k=x
        P(k)=k
    else x<0
        N(k)=k
    end
end
P
N

Best Answer

Just use ‘logical indexing’:

x=[-3.5 -5 6.2 11 0 8.1 -9 0 3 -1 3 2.5];
P = x(x >= 0);
N = x(x < 0);

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MATLAB: How to use a for loop to return a vector

Hi Adam,

you actually don't need a loop:

P = x(x > 0);
N = x(x < 0);
P =
      6.2000   11.0000    8.1000    3.0000    3.0000    2.5000
N =
     -3.5000   -5.0000   -9.0000   -1.0000

If you want to use a loop, you need to assign an index to P and N, otherwise the loop will erase the current value at every iteration. Here's an example;

P = zeros(1,length(x)); % Initialize a vector P of length equal to that of x. After the loop we get rid of the 0 values.

N = P; same thing for N.

for k=1:length(x)
      if x(k)>0 
          P(k) =x(k);
      elseif x(k)<0
          N(k)=x(k);
      end
  end
P(P==0) = []; % Remove values equal to 0
N(N==0) = [];

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What you're calling the Euclidean distance is the RMS difference in intensity between the two images. And that (and PSNR and MSE) is not such a great way to compare images anymore, unless you're looking for a fairly exact match - like you know for a fact that the test image is definitely one of the database images. You'll probably find SSIM is used more often: http://en.wikipedia.org/wiki/SSIM. But I can't run your code because I don't have the Wavelet Toolbox. I've added it to the product list to alert anyone else who might try to run your code.

Best Answer

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