Trace of Extrinsic Curvature

The trace of the extrinsic curvature at each point on the grid is placed in the grid function trK. The algorithm for calculating the trace uses the physical metric, that is it includes any conformal factor.

$${\tt trK} \equiv tr K = \frac{1}{\psi^4} g^{ij} K_{ij}$$ (part221)