[ET Trac] [Einstein Toolkit] #1906: CarpetRegrid2: possible off-by-one error when using regrid_every parameter

[Einstein Toolkit]

#1906: CarpetRegrid2: possible off-by-one error when using regrid_every parameter
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  Reporter:  bmundim  |       Owner:  eschnett           
      Type:  defect   |      Status:  new                
  Priority:  major    |   Milestone:                     
 Component:  Carpet   |     Version:  development version
Resolution:           |    Keywords:  CarpetRegrid2      
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Comment (by eschnett):

 It is possible that there is an off-by-one error, however:

 The first iteration, right after setting up initial conditions, is
 iteration 1. Regridding occurs before the evolution step, and thus the
 first time it can occur is at iteration 1 (i.e. before the first time
 step).

 Iteration 0 is setting up initial conditions. There can be regridding as
 well while setting up initial conditions, but this is governed by slightly
 different rules, so let's disregard this here.

 Maybe it is just how iterations are counted that is confusing? With two
 levels, you have:
 * it=0: initial conditions
 * it=1: coarse grid step
 * it=1: fine grid step
 * it=2: fine grid step
 * it=2: restriction to coarse grid
 * it=3: coarse grid step
 * it=3: fine grid step
 * it=4: fine grid step
 * it=4: restriction to coarse grid

 etc.

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Ticket URL: <https://trac.einsteintoolkit.org/ticket/1906#comment:1>
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