[Nek5000-users] Subroutine opdssum

[nek5000-users at lists.mcs.anl.gov]

Dear Paul,

thank you very much for your help: the answer is very clear.
I was asking that question because I have a problem with conjugate heat transfer and Low Mach number formulation (I already posted a question about that) and I was trying to understand what is going on in qthermal.f .
When at line 41 of qthermal.f the subroutine opdssum is called, ifield= 2 (temperature field), and when vec_dssum is called, gs_op_many is executed with gsh_fld(ifldt)=1 (where ifldt=ifield).
Then at line 50, ifield is changed to 1 (velocity field). After that dssum is called and gs_op is executed with gsh_fld(ifldt)= 0.
I don't understand why gsh_fld(2) is equal to 1 while gsh_fld(1) is equal to 0. What is the difference in the two operations?

Thanks in advance for your help.

With best regards,
Andrea.


-----Original Message-----
From: nek5000-users-bounces at lists.mcs.anl.gov on behalf of nek5000-users at lists.mcs.anl.gov
Sent: Tue 5/31/2011 1:10 AM
To: nek5000-users at lists.mcs.anl.gov
Subject: Re: [Nek5000-users] Subroutine opdssum
 

Dear Andreas,

gsh_fld(ifldt) refers to the gather-scatter handle for field "ifldt"

ifldt would be a flag refering to the field (1=velocity, 2=temperature, 
etc.) for which the gather-scatter (gs) operation is being performed.

At present, the situation is not entirely satisfactory because ifield
is a global variable that can be in an ambiguous state.  In the past,
opdssum (like all other "op" commands) would be applied only on a vector
field - for which there is only one mesh (or topology), namely, velocity.
In MHD, one also has the B-field but this field generally matches the
topology of the velocity.   This state of affairs will change in the near
future when we support a B-field external to the velocity field.

I hope this clarifies a bit...

Paul



On Sat, 28 May 2011, nek5000-users at lists.mcs.anl.gov wrote:

> Dear all,
>
> I was looking into the subroutine "vec_dssum", which is called in "opdssum".
> At a certain point there is a call to "gs_op_many" (a gather scatter operation I guess, isn't it?) and one of the arguments which is passed to this subroutine is "gsh_fld(ifldt)". I printed to screen the content of  "gsh_fld" but I don't understand what is the meaning of it.
>
> Thanks in advance for your help.
>
> Regards,
> Andreas.
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