[Users] Baryonic mass

[Roland Haas]

Hello Thomas,

there are basically two ways of doing this.

1. if you are using GRHydro or IllinoisGRHMD then both of then define a
variable "dens" which is the relativistic rest mass density. Asking for
a "sum" reducing of that variable computes the total rest mass *up to*
having to multiple it by the product of dx*dy*dz (ie the values you
specified in your parfile as CoordBase::dx, dy, dz). Something like
this:

CarpetIOScalar::outScalar_vars = "GRhydro::dens"
CarpetIOSCalar::outScalar_reductions = "sum"
CarpetIOScalar::outScalar_every = 1

(untested!) is what you will have to add to your parfile.

2. you can use the RestMass thorn that has just been proposed on this
mailing list:
http://lists.einsteintoolkit.org/pipermail/users/2018-November/006632.html

You can find the pull request for it on bitbucket: 

https://bitbucket.org/einsteintoolkit/einsteinanalysis/pull-requests/8/hydro_analysis-added-hydro_masses-in-order/diff

the pull request contains example parfiles for both GRHydro and
IllinoisGRMHD. If you find it useful, please contact the authors in
particular Federico Cipolletta <cipo87 at gmail.com> (who spoke up on the
mailing list) who may be interested in working with you to document
"external interest" in the modification which helps getting it into the
ET.

There have been a number of discussion relating to rest mass, is
conservation and how to measure its flux on the mailing list recently
and you may want to consult the mailing list archive or search it using
the information provided here:

https://www.einsteintoolkit.org/support.html

http://lists.einsteintoolkit.org/pipermail/users/

Yours,
Roland

> Good morning,
> 
> It would be greatly appreciated if you could give me some feedback  
> regarding the following topic.
> 
> I would like know whether it is possible to calculate the total  
> baryonic mass of the given system during the evolution within the ET (  
> maybe there is a module which I was not able to find) or I have to  
> compute it externally.
> 
> Thank you.
> 
> Sincerely,
> Theodoros Soultanis
> 
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