A multigrid algorithm for solving the multi-group, anisotropic scattering Boltzmann equation using first-order system least-squares methodology. Chang, B.; Lee, B. — 2003 ETNA. Electronic Transactions on Numerical Analysis [electronic only]
The Extension Problem for Functions Invariant under a Group. B.-Ch. Chang; J.W. Smith — 1968 Monatshefte für Mathematik