[Users] Issues with Downloading/Installing the tool kit

[Roland Haas]

Hello Joe,

> The project I am contemplating is to try to use a Mimetic approach to
> solving some of the PDEs in ETK.
> 
> Can you point me to the places in the code where PDE solutions are
> being performed?
The main PDE (that is solved as a straightforward PDE) in the Einstein
Toolkit are Einstein's equations of General Relativity which are solved
by the McLachlan thorn ML_BSSN. That thorn is actually auto-generated
from a Mathematica description of the PDE that you can find in the
file arrangements/McLachlan/m/McLachlan_BSSN.m (or so).

A simpler equation would be the scalar wave equation

(-\partial^2_t + \Delta) \phi = 0

which is our usual test case for a hyperbolic equation (the ET is
almost exclusively used for those).

There are any number of sample codes implementing this equation eg in
the CactusExamples or CactusWave arrangements or also one for Kranc
called SimpleWave.

There is also current project called NRPy+ by Zach Etienne to generate
codes for PDEs using python (https://math.wvu.edu/~zetienne/SENR/), who
is also subscribed to this list.

The other big set of PDEs in the ET are the equations of general
relativistic (magneto-)hydrodynamics ie flux conservative equations of
the form

\partial_t U + \partial_i F^i(U) = S(U)

which are highly nonlinear and prone to formming shocks. These are
solved using high-resolution, shock capturing, finite volume methods in
the thorns GRHydro and IllinoisGRMHD, providing two independent
implementations of codes to simulate relativistic hydrodynamics.

Yours,
Roland

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