[Users] About cctk_time

[Erik Schnetter]

Jay

This intermediate step comes from the time integrator. The Einstein
Toolkit usually uses Runge-Kutta type time integrators that perform
multiple sub-steps for each time step. These time integrators are
provided by the "Methods of Lines" thorn ("MoL"). The respective
documentation should have further pointers, and the respective
parameter settings should also tell you more. (See also e.g.
<https://en.wikipedia.org/wiki/Runge–Kutta_methods>).

-erik

On Tue, Nov 10, 2020 at 12:20 PM Jay Vijay Kalinani
<jayvijay.kalinani at phd.unipd.it> wrote:
>
> Dear all,
>
> I am trying to perform a magnetised TOV simulation using Einstein Toolkit and Spritz GRMHD code. In particular, currently I have a subroutine that adds a dipolar magnetic field to the TOV star after its initial data has been generated via TOVSolver thorn.
> Within this subroutine, I have added the following lines that print the 'cctk_time' value as:
>
> character(len=200) warnline
> WRITE( warnline, '( "cctk_time: ", g16.7)' ) cctk_time
> call CCTK_INFO(warnline)
>
> This subroutine is scheduled in HydroBase_Con2Prim after Con2Prim step. And I get the following lines in the .out file as:
> .........
>
> INFO (TOVSolver): Integrated TOV equation
>
> INFO (TOVSolver): Information about the TOVs used:
>
> INFO (): TOV    radius    mass  bary_mass mass(g) cent.rho rho(cgi)        K   K(cgi)    Gamma
>
> INFO ():   1   8.12502  1.40016  1.50618 2.78e+33  0.00128 7.92e+14      100 1.45e+05        2
>
> INFO (TOVSolver): Not using old matter initial data
>
> INFO (TOVSolver): Done interpolation.
>
> INFO (Spritz_DipoleAndAtmo): cctk_time:     0.000000
>
> INFO (Spritz_DipoleAndAtmo): Adding a poloidal magnetic field to the TOV star on reflevel 0
>
> INFO (Spritz_DipoleAndAtmo): Adding atmo to the TOV star on reflevel = '0'
>
> INFO (Spritz_DipoleAndAtmo): cctk_time:     0.000000
>
> -----------------------------------------------------------------------------------------------------------------------------------
>
> Iteration      Time |              ADMBASE::alp |            HYDROBASE::rho |          HYDROBASE::press |            SPRITZ::B_norm
>
>                     |      minimum      maximum |      minimum      maximum |      minimum      maximum |      minimum      maximum
>
> -----------------------------------------------------------------------------------------------------------------------------------
>
>         0     0.000 |    0.6698612    0.9603815 | 5.827798e-11    0.0012800 |    0.0000000    0.0001638 | 8.399814e-09    0.0000399
>
> INFO (Spritz_DipoleAndAtmo): cctk_time:    0.3906250E-01
>
> INFO (Spritz_DipoleAndAtmo): cctk_time:    0.3906250E-01
>
> INFO (Spritz_DipoleAndAtmo): cctk_time:    0.7812500E-01
>
> INFO (Spritz_DipoleAndAtmo): cctk_time:    0.7812500E-01
>
>         1     0.078 |    0.6698612    0.9603833 | 5.827814e-11    0.0012799 |    0.0000000    0.0001638 | 8.294987e-09    0.0000395
>
> INFO (Spritz_DipoleAndAtmo): cctk_time:    0.1171875
>
> INFO (Spritz_DipoleAndAtmo): cctk_time:    0.1171875
>
> INFO (Spritz_DipoleAndAtmo): cctk_time:    0.1562500
>
> INFO (Spritz_DipoleAndAtmo): cctk_time:    0.1562500
>
>         2     0.156 |    0.6698612    0.9603850 | 5.827829e-11    0.0012797 |    0.0000000    0.0001638 | 8.294994e-09    0.0000390
>
> ..........
>
>
>
>
> The simulation is performed in uniform grid with dx=dy=dz=0.3125, time::dtfac = 0.25 and HydroBase::timelevels = 2.
> As you may see from the output lines, in between iteration 0 which is at cctk_time=0.0 and iteration 1 which is at cctk_time=0.078125, there is an intermediate time step with 'cctk_time=0.0390625' when the subroutine is called.
>
> I was hoping to understand better why this intermediate time step exists between two consecutive iterations, and if there is any documentation I could look at.
> Any help would be much appreciated.
>
> Thank you very much.
> Sincerely,
> Jay Kalinani
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-- 
Erik Schnetter <schnetter at cct.lsu.edu>
http://www.perimeterinstitute.ca/personal/eschnetter/