[Users] Problem regriding using trigger thorn

[Dhruv Desai]

Hello,
I am running a simulation with Daniel Siegel where we use a base level
plus 6 refinement levels, like the following:
CarpetRegrid2::radius_1[1]  = 336.0    # dx/64
CarpetRegrid2::radius_1[2]  = 168.0    # dx/64
CarpetRegrid2::radius_1[3]  = 84.0    # dx/64
CarpetRegrid2::radius_1[4]  = 42.0    # dx/64
CarpetRegrid2::radius_1[5]  = 21.0    # dx/64
CarpetRegrid2::radius_1[6]  = 10.5    # dx/64

We ran simulations of a neutrino-driven wind from a Neutron star, out
to ~150 ms, and now we want to turn on a high magnetic field. We have
tried B-fields of varying strengths, but if we try a B-field strength
that is too high, we find errors generated on the innermost refinement
level boundary. We believe if we enlarge the innermost box size ie.
CarpetRegrid2::radius_1[6]  = 10.5 --> ~19-20, these errors would
disappear. But we are having trouble doing this. In our attempt, we
activate the trigger thorn with the following settings:

ActiveThorns = "Trigger"
Trigger::Trigger_Debug = 1
Trigger::Trigger_Once[0]=1
Trigger::Trigger_Number =1
Trigger::Trigger_Checked_Variable[0]="GRHydro::GRHydro_rho_min"
Trigger::Trigger_Reduction       [0]=""
Trigger::Trigger_Relation        [0]="<"
Trigger::Trigger_Checked_Value   [0]= 1.1
Trigger::Trigger_Reaction        [0]="steerparam"
Trigger::Trigger_Steered_Parameter_Value [0] = "19.32"
Trigger::Trigger_Steered_Parameter_Name  [0] = "radius_1[6]"
Trigger::Trigger_Steered_Parameter_Thorn [0] = "CarpetRegrid2"

(We use a trivially satisfied trigger condition so that the parameter
value is reset immediately upon restart.)
Since the CarpetRegrid2 variable "radius_1[6]" is not steerable, we
had to modify this to make it such. After turning debug on, we see the
following output:

INFO (Trigger): Testing triggers
INFO (Trigger): last_checked: -1
INFO (Trigger): trigger nr. 0 fulfilled for GRHydro_rho_min
(0.000000<1.100000)
INFO (Trigger): Steering parameter
INFO (Trigger): Parameter steered

Which supposedly successfully resets the value correctly. We believe
that even though this may be the case, the actual grid is not
changing. We plot the first 2 boundary levels and show them in the
attached file.

There must be interpolation of the second innermost grid onto the
innermost grid, and we believe this is not actually handled
mid-simulation and thus doesn't not result in the change we expect.

Is there any simple way of changing the inner grid easily?
Any help is much appreciated!

[image: image(1).png]


Thanks,
Dhruv Desai
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