'Introduction to sensitivity analysis approaches' (Electromagnetic Waves, 2017), 'Adjoint Sensitivity Analysis of High Frequency Structures with MATLAB®', Chap. 1, pp. 1-25, DOI: 10.1049/SBEW525E_ch1
IET Digital Library, https://digital-library.theiet.org/;jsessionid=bigr6rfqph91r.x-iet-live-01content/books/10.1049/sbew525e_ch1