[FLASH-USERS] MAG_FACE_VAR and MAGI_FACE_VAR

[Seyit Hocuk]

Hi,

You can also update the cell-centered magnetic field strengths, see 
below. Am I right in saying that it is more important to write the 
correct face centered values (MAG_FACE_VAR), as the cell-centered values 
get updatde from them?

magx(i) = some value
call Grid_putRowData(blockID, CENTER, MAGX_VAR, EXTERIOR, &
              IAXIS, startingPos, magx, sizeX)


Seyit



On 02/08/2012 09:35 PM, dongwook at flash.uchicago.edu wrote:
> Dear Nathan,
>
> As you pointed out, there are two face variables MAG_FACE_VAR and
> MAGI_FACE_VAR.
> The first one (MAG_*) is the primary face variables that store magnetic
> fields at the cell interfaces,
> and the MAGI_* is the secondary (derived) one ("I" for the intermediate).
>
> One difference between them is that MAG_ stores Bx,By,Bz at "n" states,
> whereas MAGI_ stores Bx,By,Bz at "n+1/2" states.
>
> So when you initialize face variables, you don't need to worry about
> initializing MAGI_ variable, and only need to initialize MAG_ variable in
> Simulation_initBlock.F90.
>
> Once you initialize MAG_ variable MAGI_ will then store face variables at
> the half time step (n+1/2) that are evolved from the initialized MAG_
> variable at n time step. This is done in hy_uhd_staggeredDivb.F90 routine.
>
> As MAGI_ will hold the derived secondary face variables, it won't harm to
> initialize them in
> Simulation_initBlock.F90 routine (as is done in BlastBS). MAGI_ will just
> be recalculated anyway.
>
> There is one case you want to take care of MAGI_ variable. In case you
> need a customized boundary condition for your simulation, you then need to
> apply the same boundary condition to MAGI_ variable as well. But if you
> just want to use those boundary conditions that FLASH supports already,
> you don't need to do anything for MAGI_ either.
>
> In summary, you only need to initialize MAG_ but not MAGI_. And apply your
> own use boundary condition to both MAG_ and MAGI_ variables.
>
> Hope this helps,
> Dongwook
>
> =========================================
> Dongwook Lee, Ph.D., Research Scientist
> FLASH Center for Computational Science
> University of Chicago
> 5747 S. Ellis Ave., Room 319
> (773) 834-6830
>
>> Hello all,
>>
>> I'm currently in the middle of porting a problem to use the unsplit
>> staggered mesh MHD solver included with the newest release of FLASH.
>> However, I'm unsure how to correctly the face[x,y,z] arrays in
>> Simulation_initBlock.F90.  In Flash.h there are two preprocessor macros to
>> index the first dimension of the array, MAG_FACE_VAR and MAGI_FACE_VAR.
>> Some of the example initBlock routines (e.g. OrszagTang) in the magnetoHD
>> directory only set MAG_FACE_VAR, leaving the MAGI_FACE_VAR entries zero.
>> Others (e.g. BlastBS) set both the MAG_FACE_VAR and MAGI_FACE_VAR entries.
>>
>> I'm curious why there are two face variables - and what the difference is.
>>   I'm also curious whether I should set one or both when I set up my
>> problem.
>>
>> Thanks very much for your help with this!
>>
>> Best,
>>
>> Nathan Goldbaum
>> Graduate Student
>> Astronomy&  Astrophysics, UCSC
>> goldbaum at ucolick.org
>> http://www.ucolick.org/~goldbaum
>>