ZG control for nonlinear system 2-output tracking with GD used additionally once more

In this paper, the Zhang-gradient (ZG) method, which is a combination of Zhang dynamics (ZD) and gradient dynamics (GD) methods, is presented for solving the tracking control problem of a difficult example system with one control input fixed. Instead of using GD twice more, we only use GD once more for this system in the paper. Besides, simulation verifications further illustrate that the proposed controller group based on the ZG method with GD used additionally once more can achieve relatively satisfactory tracking success and accuracy.