I'm I right in thinking that a Vaidya metric made by taking the Schwarzchild solution in in going Eddington–Finkelstein coordinates and replacing the mass M with a function M(v) describes an in flux of energy where as going to out going Eddington–Finkelstein coordinates and replacing M with M(u) describes an out flux of energy. So if I was modelling the collapse of a black hole I would use M(v) where dM/dv is positive and equal the the flux. I wanted to model a radiating star I would use M(u) with dM/du negative. But for a radiating black hole I could use M(v) with dM/dv negative i.e. an influx of negative energy?