Subroutines to Define Useful Derived Data Types

Case 3. One process sends and receives; the other receives and sends It is always safe to order the calls of MPI_(I)SEND and MPI_(I)RECV so that a

2.5 Derived Data Types

2.5.2 Subroutines to Define Useful Derived Data Types

In parallelizing programs, you often need to send and receive elements of a submatrix that are not contiguous in memory. This section provides four utility subroutines to define the most typical derived data types that you might want to use in your programs. These subroutines are not part of the MPI library and are not supported by IBM.

Figure 23. A Submatrix for Transmission

Suppose you want to send data in the shaded region in Figure 23 on page 30. By using the utility subroutine para_type_block2a or para_type_block2 described below, the code becomes very neat:

CALL para_type_block2a(2, 7, 2, 5, MPI_REAL, itype)

CALL MPI_SEND(a(3,1), 1, itype, idst, itag, MPI_COMM_WORLD, ierr)

CALL para_type_block2(2, 7, 0, 3, 4, 1, 5, MPI_REAL, itype2) CALL MPI_SEND(a, 1, itype2, idst, itag, MPI_COMM_WORLD, ierr)

The meanings of parameters are clarified in the following sections. The source code for these subroutines is also included, as well as three dimensional

versions. When you use the data type defined by para_type_block2a, specify the initial address of the submatrix,^a(3,1), as the address of the send buffer. On the other hand, in using para_type_block2, specify the initial address of the matrix,a or^a(2,0), as the address of the send buffer.

2.5.2.1 Utility Subroutine: para_type_block2a

Parameters

INTEGER imin The minimum coordinate value of the first dimension INTEGER imax The maximum coordinate value of the first dimension INTEGER ilen The length of the rectangle in the first dimension INTEGER jlen The length of the rectangle in the second dimension INTEGER ioldtype The data type of the elements in the rectangular area INTEGER inewtype The newly defined derived data type

Figure 24. Utility Subroutine para_type_block2a

Source code

SUBROUTINE para_type_block2a(imin, imax, ilen, jlen,

& ioldtype, inewtype)

INCLUDE ’mpif.h’

CALL MPI_TYPE_VECTOR(jlen, ilen, imax - imin + 1, CALL para_type_block2a(imin, imax, ilen, jlen, ioldtype,

inewtype) Usage

& ioldtype, inewtype, ierr) CALL MPI_TYPE_COMMIT(inewtype, ierr)

END

2.5.2.2 Utility Subroutine: para_type_block2

Parameters

the first dimension

INTEGER iend The maximum coordinate value of the rectangular area in the first dimension

INTEGER jsta The minimum coordinate value of the rectangular area in the second dimension

INTEGER jend The maximum coordinate value of the rectangular area in the second dimension

INTEGER ioldtype The data type of the elements in the rectangular area INTEGER inewtype The newly defined derived data type

Figure 25. Utility Subroutine para_type_block2

Source code

SUBROUTINE para_type_block2(imin, imax, jmin,

& ista, iend, jsta, jend,

& ioldtype, inewtype)

INCLUDE ’mpif.h’

INTEGER iblock(2), idisp(2), itype(2)

CALL para_type_block2(imin, imax, jmin, ista, iend, jsta, jend, ioldtype, inewtype)

Usage

CALL MPI_TYPE_EXTENT(ioldtype, isize, ierr) ilen = iend - ista + 1

jlen = jend - jsta + 1

CALL MPI_TYPE_VECTOR(jlen, ilen, imax - imin + 1,

& ioldtype, itemp, ierr)

iblock(1) = 1 iblock(2) = 1 idisp(1) = 0

idisp(2) = ((imax-imin+1) * (jsta-jmin) + (ista-imin)) * isize itype(1) = MPI_LB

itype(2) = itemp

CALL MPI_TYPE_STRUCT(2, iblock, idisp, itype, inewtype, ierr) CALL MPI_TYPE_COMMIT(inewtype, ierr)

END

2.5.2.3 Utility Subroutine: para_type_block3a

Parameters

INTEGER imin The minimum coordinate value of the first dimension INTEGER imax The maximum coordinate value of the first dimension INTEGER jmin The minimum coordinate value of the second dimension INTEGER jmax The maximum coordinate value of the second dimension INTEGER ilen The length of the rectangular solid in the first dimension INTEGER jlen The length of the rectangular solid in the second dimension INTEGER klen The length of the rectangular solid in the third dimension INTEGER ioldtype The data type of the elements in the rectangular solid INTEGER inewtype The newly defined derived data type

CALL para_type_block3a(imin, imax, jmin, jmax, ilen, jlen, klen, ioldtype, inewtype)

Usage

Figure 26. Utility Subroutine para_type_block3a

Source code

SUBROUTINE para_type_block3a(imin, imax, jmin, jmax,

& ilen, jlen, klen,

& ioldtype,inewtype)

INCLUDE ’mpif.h’

CALL MPI_TYPE_EXTENT(ioldtype, isize, ierr) CALL MPI_TYPE_VECTOR(jlen, ilen, imax - imin + 1,

& ioldtype, itemp, ierr)

idist = (imax - imin + 1) * (jmax - jmin + 1) * isize

CALL MPI_TYPE_HVECTOR(klen, 1, idist, itemp, inewtype, ierr) CALL MPI_TYPE_COMMIT(inewtype, ierr)

END

2.5.2.4 Utility Subroutine: para_type_block3

Parameters

INTEGER imin The minimum coordinate value of the first dimension INTEGER imax The maximum coordinate value of the first dimension

CALL para_type_block3(imin, imax, jmin, jmax, kmin, ista, iend, jsta, jend, ksta, kend, ioldtype, inewtype) Usage

INTEGER jmin The minimum coordinate value of the second dimension INTEGER jmax The maximum coordinate value of the second dimension INTEGER kmin The minimum coordinate value of the third dimension INTEGER ista The minimum coordinate value of the rectangular solid in

the first dimension

INTEGER iend The maximum coordinate value of the rectangular solid in the first dimension

INTEGER jsta The minimum coordinate value of the rectangular solid in the second dimension

INTEGER jend The maximum coordinate value of the rectangular solid in the second dimension

INTEGER ksta The minimum coordinate value of the rectangular solid in the third dimension

INTEGER kend The maximum coordinate value of the rectangular solid in the third dimension

INTEGER ioldtype The data type of the elements in the rectangular solid INTEGER inewtype The newly defined derived data type

Figure 27. Utility Subroutine para_type_block3

Source code

SUBROUTINE para_type_block3(imin, imax, jmin, jmax, kmin,

& ista, iend, jsta, jend, ksta, kend,

& ioldtype, inewtype) INCLUDE ’mpif.h’

INTEGER iblock(2), idisp(2), itype(2) CALL MPI_TYPE_EXTENT(ioldtype, isize, ierr) ilen = iend - ista + 1

jlen = jend - jsta + 1 klen = kend - ksta + 1

CALL MPI_TYPE_VECTOR(jlen, ilen, imax - imin + 1,

& ioldtype, itemp, ierr)

idist = (imax-imin+1) * (jmax-jmin+1) * isize

CALL MPI_TYPE_HVECTOR(klen, 1, idist, itemp, itemp2, ierr) iblock(1) = 1

iblock(2) = 1 idisp(1) = 0

idisp(2) = ((imax-imin+1) * (jmax-jmin+1) * (ksta-kmin)

& + (imax-imin+1) * (jsta-jmin) + (ista-imin)) * isize itype(1) = MPI_LB

itype(2) = itemp2

CALL MPI_TYPE_STRUCT(2, iblock, idisp, itype, inewtype, ierr) CALL MPI_TYPE_COMMIT(inewtype, ierr)

END

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