[MITgcm-devel] changing cg2d

[Jean-Michel Campin]

Hi Martin (and Patrick),

OK, was more a detail. you guys know how to make TAF happy.

But still think that this #ifdef ALLOW_CONST_RHSMAX
is not necessary if we don't normalise the RHS, which is the case when 
using cg2dTargetResWunit (instead of cg2dTargetResidual).
It has been added to the code quiet a long time ago (~5-6 years),
it works (few verification exp use it), and it's cleaner than
this ALLOW_CONST_RHSMAX because you can choose it even when not 
using MPI or not in the backward mode.

Cheers,
Jean-Michel

On Fri, Dec 01, 2006 at 08:38:02AM +0100, Martin Losch wrote:
> Hi Jean-Michel, the cg2d_nsa (not self adjoint) is only for bottom  
> topography as a control parameter. It's based on a version of cg2d  
> around ckpt40 or so. So I am not surprised that modifications from  
> 3yrs ago did make it into this version. Likewise the  
> ALLOW_CONST_RHSMAX is necessary as long as there isn't a working  
> adjoint to global_max (which I have been to stupid to generate so  
> far). Maybe we can merge the new features of cg2d into cg2d_nsa in  
> the future?
> 
> M.
> On 1 Dec 2006, at 01:16, Jean-Michel Campin wrote:
> 
> >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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