MSC:In this paper we present a new formulation of the augmented basic interpolation problem (aBIP) with rational matrices, in terms of the stability of four rational matrices, so that the aBIP transforms into a purely linear-algebraic problem. Actually, the existing interpolation condition, given by an integral, is replaced by stability of a rational matrix. The new condition is applied to the H ∞ optimal control of one-block plants having imaginary axis invariant zeros. A new parameter in the parametrization of H ∞ optimal controllers is revealed, which is given in terms of the derivative of the closed-loop system at the imaginary axis invariant zeros of the plant. The H ∞ optimal control algorithm is illustrated by an example, and compared to the existing algorithms.