  This paper solves the sparsest feedback selection problem for linear time
invariant structured systems, a long-standing open problem in structured
systems. We consider structurally cyclic systems with dedicated inputs and
outputs. We prove that finding a sparsest feedback selection is of linear
complexity for the case of structurally cyclic systems with dedicated inputs
and outputs. This problem has received attention recently but key errors in the
hardness-proofs have resulted in an erroneous conclusion there. This is also
elaborated in this brief paper together with a counter-example.
