Defining Domain Dimensions

If the RELO macro is set, arrays are allocated at run time and the defaults for the small number of user changeable parameters in mod_dimensions.F90 are usually appropriate. The most commonly edited parameter in mod_dimensions.F90 is mxthrd which might need changing when parallelizing with OpenMP (TYPE=omp or TYPE=ompi), see the OpenMP wiki page for more details.

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If the RELO macro is not set, arrays are allocated at compile time and dimensions.h will need customizing for a new region or a different number of layers or a different TYPE. The user-tunable parameters are:

 itdm   = total grid dimension in i direction   
 jtdm   = total grid dimension in j direction   
 kdm    =       grid dimension in k direction   
 iqr    = maximum number of tiles in i direction   
 jqr    = maximum number of tiles in j direction   
 idm    = maximum single tile grid dimension in I direction   
 jdm    = maximum single tile grid dimension in j direction   
 mxthrd = maximum number of OpenMP threads   
 kkwall = grid dimension in k direction for wall relax arrays   
 kknest = grid dimension in k direction for nest relax arrays   
 kkmy25 = grid dimension in k direction for M-Y 2.5 arrays

If memory is plentifull, then kkwall,kknest,kkmy25 can all be set to kdm. However, if memory is in short supply then kwall and/or kknest can be set to 1 (if wall or nest relaxation is not being used) and if the Mellor-Yamada mixed layer isn't being used kkmy25 can be set to -1.

A new source code directory and executable is always required whenever itdm, or jtdm, or kdm change (i.e. whenever the region size or the number of layers change). Note that ../topo/regional.grid.b is used to define the region to setup programs, and needs to be consistent with dimensions.h.

A separate source code directory and executable is always required for each parallelization strategy, or TYPE, chosen (TYPE=one, or omp, or ompi, or mpi, or shmem). The TYPE also effects how dimensions.h is configured. There are examples of dimensions.h for each TYPE in ALT_CODE.

When running on a shared memory machine (TYPE=one or omp) set: iqr=jqr=1, idm=itdm, and jdm=jtdm. Note that the same OpenMP executable (TYPE=omp) can be used for a range of processor counts, provided mxthrd is chosen appropriately, see the OpenMP wiki page.

When running on a distributed memory machine (TYPE=mpi or ompi or shmem) set: iqr and jqr to the maximum number of processors used in each dimension, and idm and jdm to the maximum (worse case) dimensions for any single tile on any targeted number of processors. Note that the same executable can be used for a range of processor counts, provided iqr,jqr,idm,jdm are all large enough for each case. The mxthrd parameter is only important when using OpenMP, see the OpenMP wiki page.