Fix a bug for Nx Ny in swath grid

[metdyn]

Types of change(s)

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)
• Trivial change (affects only documentation or cleanup)

Checklist

• Tested this change with a run of GEOSgcm
• Ran the Unit Tests (make tests)

Description

In swath grid, e.g.,
im_world 135
jm_world 7851
when Ncore=3456
the default gives Nx ~ sqrt(2Ncore), Ny= Ncore /Nx
such that floor ( im_world / Nx ) = 1

function generate_new_decomp tries to correct it, but violate Nx * Ny = Ncore.
Printout below:

 bf check fill consistency
 ims            2           2           2           2           2           2
           2           2           2           2           2           2
           2           2           2           2           2           2
           2           2           2           2           2           2
           2           2           2           2           2           2
           2           2           2           2           2           2
           2           2           2           2           2           2
           2           2           2           2           2           2
           2           2           2           2           2           2
           2           2           2           2           2           2
           2           2           2           1           1           1
           1           1           1           1           1           1
 jms          164         164         164         164         164         164
         164         164         164         164         164         164
         164         164         164         164         164         164
         164         164         164         164         164         164
         164         164         164         163         163         163
         163         163         163         163         163         163
         163         163         163         163         163         163
         163         163         163         163         163         163
 im_world          135
 jm_world         7851
 af  this%generate_newnxy
 af check fill consistency
 ims            4           4           4           4           4           4
           4           4           4           4           4           4
           4           4           4           4           4           4
           4           4           4           4           4           4
           4           4           4           3           3           3
           3           3           3           3           3           3
 jms          164         164         164         164         164         164
         164         164         164         164         164         164
         164         164         164         164         164         164
         164         164         164         164         164         164
         164         164         164         163         163         163
         163         163         163         163         163         163
         163         163         163         163         163         163
         163         163         163         163         163         163
 im_world          135
 jm_world         7851

Related Issue

[tclune]

I will approve, but you might want to look at how domain decomposition is done in MAPL3 for this problem:

MAPL/geom_mgr/latlon/LatLonDecomposition_smod.F90

Lines 29 to 36 in 44dfddf

	associate (aspect_ratio => real(dims(1))/dims(2))
	nx_start = max(1, floor(sqrt(petCount * aspect_ratio)))
	do nx = nx_start, 1, -1
	if (mod(petcount, nx) == 0) then ! found a decomposition
	exit
	end if
	end do
	end associate

[metdyn]

Thanks. I have added a note to indicate using the same algorithm from above. I am checking if this modification works for 124416 cores.

[metdyn]

I am able to run MAPL C720 with ncore=3456, not specifying NX and NY for swath.
This setup will accomodate the 6hr Epoch swath running on 100,000 cores.

CS grid:           NX: 24 ;   NY: 144
        sampler: DEBUG: Xdim, Ydim   96 8100
        sampler: DEBUG:  nx, ny (check_and_fill_consistency) =     48     72
        sampler: DEBUG: Xdim, Ydim  135 8051
        sampler: DEBUG:  nx, ny (check_and_fill_consistency) =     64     54
        sampler: DEBUG: Xdim, Ydim  135 7851
        sampler: DEBUG:  nx, ny (check_and_fill_consistency) =     64     54