How to ignore values in a matrix that is out of bound when performing column 'find' in an array?

Z is a 1024X1024 matrix containing negative value in some pixels.

For each pixel in Z, I need to find the column from an array 0,5,10,15,20,25,30,35,40; Because of out of bound values existing in Z matrix, I get this error 'Subscript indices must either be real positive integers or logicals.' How do I set all the negative values in matrix Z to '0' or is there a way to get around this problem? Below is the code.

m=1024;
n=1024;
Th = (0,5,10,15,20,25,30,35,40);
i=1:length(Th)
ratioAB(:,:,i)=A./B   % A and B are matrices for each Th

RF=ones(m,n);
for i=1:m
    for j=1:n
        Z2=Z(i,round(j));

col = find(Th > Z2,1,'first')-[1 0]
RF(i,j)= diff(cat(3,ratioAB(i,j,col)),[],3)/diff(Th(col))*(Z2 Th(col(1)))+ratioAB(i,j,col(1));

    end
end

[Image Analyst]

Lots of syntax errors, like in the definition of Th and RF. Plus what's with the definition of col? You're defining it as a scalar minus a 1 by 2 array. That's not a column number like you said you want.

[Yun Inn]

I have eight thicknesses, Th=0,5,10,15,20,25,30,35,40. For each of the Th, I have matrix, ratioAB.

Then, I have Z that is a 2D matrix consisting of pixels with different thicknesses. For each of the pixel, I need to find the correct ratioAB depending on the thickness. The result, RF, should be a matrix of ratioAB.

Because the Th range from 0 to 40, when I have negative value or value more than 40 in the Z matrix, I get the error 'Subscript indices must either be real positive integers or logicals.'

How do I fix the code?

Answer 1

[Matt Fig]

Z = max(Z,0)

[Azzi Abdelmalek]

very nice

[Matt Fig]

Thanks, Azzi!

Answer 2

[Azzi Abdelmalek]

 Z(find(Z<0))=0

[Matt Fig]

Or just:

Z(Z<0) = 0

No need for FIND...