Impulse-response of a linear differential operator: L_x G(x,x') = δ(x-x'). Convolution with the source then solves Lu = f. Foundational across electromagnetism, quantum field theory propagators, and many-body physics.
Impulse-response of a linear differential operator: L_x G(x,x') = δ(x-x'). Convolution with the source then solves Lu = f. Foundational across electromagnetism, quantum field theory propagators, and many-body physics.