19.3: Demystifying relaxation in the gun code algorithm

The relaxation parameter affects the convergence rate of a gun code simulation, and hence its accuracy or speed. Yet the parameter is a mystery to many gun code users. This work removes some of the relaxation parameter's mystique by providing some useful explanations and guidance derived from 1-d studies but also checked in 2-d and 3-d MICHELLE simulations. With this knowledge a user could, for example, significantly reduce the computational cost of an expensive finely-resolved 3-d sheet beam gun simulation.