Estimating phase space.
This option was removed in 2023. The reason was that although the volume of phase space occupied by a set of rays when they are initially created usually has an approximately uniform density, and also the volume of phase space occupied by the particles remains constant, according to Liouville's theorem, it has been noticed that the density of the phase space usually becomes markedly non-uniform by the time the rays reach their destination. It is therefore not possible to give reliable or meaningful information on the phase space, beyond the information that is already available in the ray output file.