Farooqi , AsmaAhmad , Riaz and Feng , Zhenping. (2020). An Improved Hybrid Adjoint Method in External Aerodynamics Using Variational Technique for the Boundary Integral Based Optimal Objective Function Gradient. Numerical Mathematics: Theory, Methods and Applications. 13 (3). 689-718. doi:10.4208/nmtma.OA-2019-0087