[Developers] HydroBase update

Frank Loeffler knarf at cct.lsu.edu
Sun Dec 6 19:58:43 CST 2009


Hi,

On Sun, Dec 06, 2009 at 07:27:16PM -0600, Erik Schnetter wrote:
> I suggest to add a parameter "initial_hydro" with a default setting of "vacuum".  This parameter, which can be extended by hydro initial data thorns, determines which hydro thorn is setting up initial data.  The default setting "vacuum" is implemented by HydroBase itself, setting all hydro variables to zero.  This corresponds to a vacuum, without atmosphere.

As long as ADMBase is used together with HydroBase initial data thorns
can use ADMBase::initial_data for this purpose, and that is what they do
at the moment.

While HydroBase itself is independend of ADMBase, hydro initial data
thorns usually do not only set the hydro variables, but also the
spacetime variables. They are wired to both, ADMBase and HydroBase. That
said, this does not have to be like this, it is simply the current
state. I am not aware of any hydro initial data thorn which can provide
initial data for the ADM system _and_ another spacetime system.

Introducing a new parameter in HydroBase would mean the need to set
an extra parameter in every hydro parameter file. In most cases a
failure to do this (e.g. using an old parameter file) could be caught
by the initial data thorn itself (looking at both parameters and refusing
to work with an incompatible combination).

In short I agree that it would make HydroBase cleaner. But it
would also require changes to both: other code and parameter files. Now
the question is if it is worth the effort. What would we gain from the
change? If the main reason for this parameter would be to ensure that
the variables are initialized, this could be done unconditionally by
HydroBase before the initial data thorns touch them. This would be
transparent to both other thorns and parameter files.

Frank

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