Discussion on applying tortoise coordinates to a dynamical Vaidya black hole
从乌龟坐标在动态Vaidya黑洞上的推广谈起

Applying generalized tortoise coordinates with undetermined parameters to a dynamical Vaidya black hole, we find the interesting condition for reducing the wave function into its standard form without divergence. It is shown that the Damour-Ruffini method with tortoise coordinate can be applied only to the event horizon rather than the apparent horizon in a dynamical space time.