[ET Trac] [Einstein Toolkit] #1554: Want to define constants in parameter files

[Einstein Toolkit]

#1554: Want to define constants in parameter files
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  Reporter:  eschnett     |       Owner:  sbrandt            
      Type:  enhancement  |      Status:  assigned           
  Priority:  major        |   Milestone:                     
 Component:  Cactus       |     Version:  development version
Resolution:               |    Keywords:                     
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Comment (by rhaas):

 Replying to [comment:6 eschnett]:
 > I want to write a parameter file that can run with multiple resolutions.
 Changing the resolution requires changes in multiple places, including
 grid size, time step size, and output frequency. Most of these values have
 a non-trivial dependency on the resolution.

 Independent of the topic of the current ticket: Cactus should allow the
 resolution to be all specifiable via a single parameter (eg ncells_[xyz]),
 shouldn't it? The timestep should be given by the Courant factor though
 Llama breaks this (I think I actually do have a patch for this somewhere).
 Output frequency can be specified by out_dt which does not depend on the
 iteration number (but may be prone to numerical roundoff issues). Search
 frequencies are likely fine if given as every_iteration (usually I want:
 everytime the second-to-finest level executes or at the the same time that
 the finest level enclosing the NS is updated). Other codes go to great
 length to provide output at times independent of the time step size and
 will interpolate the state vector to any desired output time if required
 which may be overkill (and very hard) for our AMR based infrastructure. If
 there are parts of the parfile (other than ncellss or dx) that change with
 resolution then I would try and add functionality to avoid them. Please
 keep in mind though that this is not really related to this ticket.
 Variables could also be used eg to produce a series of extraction radii
 whose size is all tied to the same variable.

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Ticket URL: <https://trac.einsteintoolkit.org/ticket/1554#comment:11>
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