％ 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.