J. Rohn et V. Kreinovich, COMPUTING EXACT COMPONENTWISE BOUNDS ON SOLUTIONS OF LINEAR-SYSTEMS WITH INTERVAL DATA IS NP-HARD, SIAM journal on matrix analysis and applications, 16(2), 1995, pp. 415-420
We prove that it is NP-hard to compute the exact componentwise bounds
on solutions of all the linear systems that can be obtained from a giv
en linear system with a nonsingular matrix by perturbing all the data
independently of each other within prescribed tolerances.