"where $\\alpha$ is the lapse function, $\\beta^i$ the shift vector and $\\gamma_{ij}$ the induced metric on the spatial hypersurfaces, which in the constrained formulation adopted by GRAMSES is approximated by a conformally-flat metric, i.e.\n",
"\n",
"\\begin{equation}\n",
"\\gamma_{ij}=\\psi^4\\delta_{ij}\n",
"\\end{equation}\n",
"with $\\psi$ being the conformal factor and $\\delta_{ij}$ the Kronecker delta. \n",
"\n",
"### Matter sources\n",
"\n",
"The usual matter source terms defined in the 3+1 formalism are given by the following projections of the energy-momentum tensor:\n",
"In these, ${\\bf x}$ is a (discrete) position vector on the cartesian simulation grid and the proportionality symbol in each equation stands for the standard cloud-in-cell (CIC) weights used for the particle-mesh projection. From these we have the following useful relations:\n",
where $\alpha$ is the lapse function, $\beta^i$ the shift vector and $\gamma_{ij}$ the induced metric on the spatial hypersurfaces, which in the constrained formulation adopted by GRAMSES is approximated by a conformally-flat metric, i.e.
\begin{equation}
\gamma_{ij}=\psi^4\delta_{ij}
\end{equation}
with $\psi$ being the conformal factor and $\delta_{ij}$ the Kronecker delta.
### Matter sources
The usual matter source terms defined in the 3+1 formalism are given by the following projections of the energy-momentum tensor:
In these, ${\bf x}$ is a (discrete) position vector on the cartesian simulation grid and the proportionality symbol in each equation stands for the standard cloud-in-cell (CIC) weights used for the particle-mesh projection. From these we have the following useful relations: