Given a feasible solution, the inverse optimization problem is to modify so
me parameters of the original problem as little as possible, and sometimes
also with bound restrictions on these adjustments, to make the feasible sol
ution become an optimal solution under the new parameter values. So far it
is unknown that for a problem which is solvable in polynomial time, whether
its inverse problem is also solvable in polynomial time. In this note we a
nswer this question by considering the inverse center location problem and
show that even though the original problem is polynomially solvable, its in
verse problem is NP-hard.