A boundary gradient search technique is introduced. The technique generates a sequence of points on the boundary of the feasible region converging to a fixed point. The gradient of the boundary at this fixed point has a prespecified directional ratio. The boundary search technique is exploited in a modification of the ellipsoidal technique for design centering. This modification allows the use of double-sided ellipsoidal sections instead of single-sided ellipsoidal sections. It improves the speed of convergence of the ellipsoidal technique. Also, a computationally inexpensive technique of determining the gradient of the gain constraints is introduced. Practical examples are given to demonstrate the new technique.

A technique for design centering and feasible region approximation that is based on generating a sequence of ellipsoids of decreasing volume and preserves the property of containing a bounded convex feasible region is introduced. The technique converges to an ellipsoid the center of which is the proposed design center. The ellipsoid matrix can be used to give what is called a preferable covariance matrix, assuming a multinormal distribution of parameters. This covariance matrix is preferred since it significantly increases the production yield for the feasible region under consideration. In addition, an ellipsoidal region approximation can be obtained by scaling the final ellipsoid, which allows an inexpensive yield estimate using the Monte Carlo method. Numerical and practical examples are considered.>