[MITgcm-devel] changing cg2d

[Jean-Michel Campin]

Hi,

I will make the changes in cg2d.F

Patrick:
We also have a 2nd version, cg2d_nsa.F, that I don't feel like changing:
I noticed that when it was checked-in (~6.month ago), did not have 
the latest changes from cg2d.F (from about the last 3.yrs), and it 
will continue.
Just one thing, when using cg2dTargetResWunit (instead of 
cg2dTargetResidual), the RHS is not normalised, which is pretty
much what the "#ifdef ALLOW_CONST_RHSMAX" is doing.

Jean-Michel

On Wed, Nov 29, 2006 at 08:44:23PM -0500, Jean-Michel Campin wrote:
> Hi Chris,
> 
> I was wondering if pre-computing the diagnonal term of the 
> 2.D solver in ini_cg2d (like I did for cg3d.F, version 1.17 versus 1.16) 
> could speed up the solver (or at least, not make it slower) ?
> 
> Here it will be only one additional 2-D array (aC2d) to store,
> will reduce the memory acces in cg2d (no acces to rA, recip_Bo)
> and reduce the number of floating point operations
> since lines 175 to 180:
>      &    -aW2d(I  ,J  ,bi,bj)*cg2d_x(I  ,J  ,bi,bj)
>      &    -aW2d(I+1,J  ,bi,bj)*cg2d_x(I  ,J  ,bi,bj)
>      &    -aS2d(I  ,J  ,bi,bj)*cg2d_x(I  ,J  ,bi,bj)
>      &    -aS2d(I  ,J+1,bi,bj)*cg2d_x(I  ,J  ,bi,bj)
>      &    -freeSurfFac*_rA(i,j,bi,bj)*recip_Bo(i,j,bi,bj)*
>      &     cg2d_x(I  ,J  ,bi,bj)/deltaTMom/deltaTfreesurf*cg2dNorm
> will be replaced by just:
>      &    +aC2d(I  ,J  ,bi,bj)*cg2d_x(I  ,J  ,bi,bj)
> 
> and same thing for lines 302-307
> 
> The reason I am asking this, is that for the deep atmosphere,
> to make it "right" in p-coordinate with topography,
> the area "rA" has to be scaled at the surface level kSurfC(i,j,bi,bj)
> -> indirect indexing -> might not be efficient.
> If we decide to change cg2d.F and store the diagnonal term, 
> now will be a good time.
> 
> Jean-Michel
> 
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