％ COMPDIR Computes a search direction in a subspace defined by Z.
％ Helper function for NLCONST.
％ Returns Newton direction if possible.
％ Returns random direction if gradient is small.
％ Otherwise, returns steepest descent direction.
％ If the steepest descent direction is small it computes a negative
％ curvature direction based on the most negative eigenvalue.
％ For singular matrices, returns steepest descent even if small.
