Lagrangian Tracers

Located in physflux(Finalize) is a routine which handles the fluxes for the Lagrangian Tracers. The routine is an upwinded Van Leer advection scheme that solves the following equation:

\frac{df}{dt}=-u \frac{df}{dx}$

You will notice that this is simply the form for a Lagrangian derivative (hence the name Lagrangian Tracer). The routine is second order in time and will maintain discontinuities to with in about 5 zones on a fixed grid.

The code works by replacing the tracer fluxes computed during the execution of numflux with the new tracers computed by the Lagrangian scheme. The scheme can be turned on by manipulating the iLTracer variable in physics.data. This routine is currently set up such that it will change all variables labeled as such into Lagrangian Tracers.

This piece of code was adapted from the MHD-TVD code originally developed by Ryu et.al.. If you have any further questions contact a member of the Minnesota Computational Astrophysics Group.