Bona--Masso slicing condition

The Bona--Masso family is $({\partial }_t-{\beta }^i{\partial }_i)\alpha =-{\alpha }^{2}f(\alpha )K$. Harmonic slicing is the choice $f=1$.

For the stationary conformally flat Schwarzschild slicing with areal radius $R=r+M$, lapse $\alpha =r/(r+M)$, and radial shift ${\beta }^r=Mr/(r+M{)}^2$, the Bona--Masso condition selects