This is a basic MATLAB operation. It is for instructional purposes.

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You may already know how to find the logical indices of the elements of a vector that meet your criteria.

This exercise is for finding the index of indices that meet your criteria. The difference is this:

     vec = [11 22 33 44];
  thresh = 25;
      vi = (vec > thresh)

vi =

     0     0     1     1

What we are looking for now is how to get the values

   x =

     3     4

Because those are the indices where the binary comparison is true.

Check out find.

Given a vector, vec, return the indices where vec is greater than scalar, thresh.