Lagrangian Optics

Ingeometrical optics, light propagation is analyzed in terms of light rays which define the path of propagation of light energy in the limitof the optical wavelength tending to zero. Many features oflight propagation can be analyzed in terms ofrays,ofcourse, subtle effects near foci, caustics or turning points would need an analysis based on the wave natureoflight. Allofgeometric optics can be derived from Fermat's principle which is an extremum principle. The counterpart in classical mecha...