"ind=[2,1] is coming which is wrong."
It is correct.
The input to sort() only has 2 elements, so the expectation to get [3 1] as the output is misplaced -
Omega=[1.528 -1.528 0.792 -0.792];
Omega(Omega>=0)
I assume you want to get the indices of these particular values from the original array, in that case, try this -
NN=sort(Omega(Omega>=0))
[~,idx] = ismember(NN,Omega)
However, the values here are obtained directly from the original array via indexing, so ismember() works here.
