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.