MATLAB: Strange problem with function ‘find’

findMATLABprecision tolerance

Hello. I have a strange problem with function find. I have this function in for loop and I use it eg. 50 times. This function not always find what I am looking for although if I run this outside the loop it will find my value.
Code:
for i=1:n,
      fid=fopen(names(i,1).name);
      spec=cell2mat(textscan(fid,'%f %f'))'; 
      fclose(fid);
      X=spec(1,:);
      Y=spec(2,:);
      for j=1:size(setX,1),
          x=setX(j,1);
          [M,N]=find(X==x);   - problem sometimes in this place
          if(isempty(M))
          DataX(j,i)=0;
          else
          DataX(j,i)=Y(M,N);
          end
      end
  end
Also I will show you the Data X file (in this place Data Y but it's the same problem – same data).
You can see that in 30 ,33 and 37 loop it didn't find the X value but this value exist and the pattern is the same as others. What it the problem?

Best Answer

Use a tolerance to allow for floating point errors,
 [M,N]=find(abs(X-x)<=somethingsmall)
where "somethingsmall" is small but >0
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