RGX_Find_Task_Grid_Ngbrs

Determine the task IDs of the nearest neighbors of local task grid

Synopsis


int RGX_Find_Task_Grid_Ngbrs(
                              MPI_Comm  Comm,
                              int       Ndim,

                              int       Ngbrs[]
                            )
/*
    In Fortran :
       Ngbrs(1,1) = Ngbr_left, Ngbrs(2,1) = Ngbr_right
       Ngbrs(1,2) = Ngbr_top , Ngbrs(2,2) = Ngbr_bottom
       Ngbrs(1,3) = Ngbr_in  , Ngbrs(2,3) = Ngbr_out
    In C:
       Ngbrs[ 0 ] = Ngbr_left, Ngbrs[ 1 ] = Ngbr_right
       Ngbrs[ 2 ] = Ngbr_top , Ngbrs[ 3 ] = Ngbr_bottom
       Ngbrs[ 4 ] = Ngbr_in  , Ngbrs[ 5 ] = Ngbr_out
*/

Unmodified Input Variables

Comm - Input Communicator of all the tasks involved.
Ndim - Dimensionality of the Grid (Integer).

Modified Output Variables

Ngbrs - Integer Array, of size 2 x Ndim, of the task ID of the local task grid's nearest neighbors. It is implicitly assumed to be declared like Ngbrs[ Ndim ][ 2 ].
returned value - returns MPI_SUCCESS if completed successfully.

Notes on Fortran Interface

The RGX routines which have this message have a Fortran interface. If the C function that is defined here has a returned integer status, the Fortran interface will have an additional argument, ierr, at the end of its argument list.

Notes on Minimal Set of Variables

In order to use RGX for a regualr grid calculation. There is a minimal set of variables needed to be used with the RGX_XXX routines. The set of variables is listed as follows,


   const int     MD_type = MPI_DOUBLE_PRECISION;
   double       *Task_xGrid;         // Data of Local Task Grid              
   int           Ndim;               // Dimensionality of the 
   //                                // grid           
   MPI_Comm      RGX_Comm;           // Communicator of all 
   //                                // sub-grids        
   int           N_task;             // No. of process/tasks 
   //                                // in Communicator 
   int          *Glb_Grid_sz;        // Global grid sizes :
   //                                // Glb_Grid_sz(Ndim) 
   int          *task_Ngbrs;         // the tid of the nearest
   //                                // neighbor task :
   //                                // task_Ngbrs(2, Ndim)                
   int          *task_Grid_endpts;   // local sub-grid's end
   //                                // points :
   //                                // task_Grid_endpts(Ndim, 2)          
   int          *N_task_1dims;       // No of task 
   //                                // per dimension :             
   //                                // N_task_1dims(Ndim)                 
   int          *stride_width;       // width of the stride of
   //                                // ghost point :
   //                                // stride_width(Ndim)                 
   MPI_Datatype *task_bndry_strides; // local task/grid's 
   //                                // boundary strides :
   //                                // task_bndry_strides(Ndim)           

Memory for each of these pointer variables can be allocated dynammically/statically, but it has to be continuous.

Supported Data Type of the Block Array

There are currently 5 datatypes supported in RGX. The types are identified by MPI_Datatype. They are MPI_INTEGER, MPI_REAL, MPI_DOUBLE_PRECISION, MPI_COMPLEX and MPI_DOUBLE_COMPLEX.

Definition Location

This subroutine is defined in the librgx.a.

Location:../src/librgx/RGX_Find_Task_Grid_Ngbrs.c