'Introduction to FDTD' (Electromagnetic Waves, 2017), 'Adjoint Sensitivity Analysis of High Frequency Structures with MATLABĀ®', Chap. 2, pp. 27-48, DOI: 10.1049/SBEW525E_ch2 IET Digital Library, https://digital-library.theiet.org/;jsessionid=6rx67f9rulms.x-iet-live-01content/books/10.1049/sbew525e_ch2