C
C  Open Systems Laboratory
C  http://www.lam-mpi.org/tutorials/
C  Indiana University
C
C  MPI Tutorial
C  Lab - Datatypes
C
C  Mail questions regarding tutorial material to lam at lam dash mpi dot org
C
C  Create a datatype called submatrix that consists of elements in
C  alternate rows and alternate columns of the given original matrix.
C
C  Use MPI_SENDRECV to send the submatrix to itself and print the
C  results. To test this program you can run the program on just
C  one processor.
C
C  For example, if the given matrix is:
C
C  1  2  3   4  5  6
C  7  8  9  10 11 12
C  13 14 15 16 17 18
C  19 20 21 22 23 23
C  24 25 26 27 28 29
C
C  The submatrix created should look like:
C
C  1   3  5
C  13 15 17
C  24 26 28
C 
      program main
      include 'mpif.h'
      
      integer ierr
      integer rank
      integer i, j
      integer a(10,10), c(5,5)
      integer subrow, submatrix 
      integer status 
      integer sizeofint
      integer blocks, blocksize, stride, bytes, numsend, numrecv
      integer tag

      call MPI_INIT(ierr)
      call MPI_COMM_RANK(MPI_COMM_WORLD, rank, ierr)
  
C     Initialize the local array 
      do 10 i = 1, 10
         do 20 j = 1, 10
            a(i, j) = (i - 1) * 10 + j
 20      continue
 10   continue

      do 31 i = 1, 10
         do 41 j = 1, 10
            print *, a(i, j)
 41      continue
 31   continue
  
C     Create a submatrix datatype 

      call MPI_TYPE_EXTENT(MPI_INTEGER, sizeofint, ierr) 
  
C     Create datatype for the sub-row 

      blocks = 5
      blocksize = 1
      stride = 2

      call MPI_TYPE_VECTOR(blocks, blocksize, stride, MPI_INTEGER, 
     &     subrow, ierr) 
      call MPI_TYPE_SIZE(subrow, bytes, ierr)
      print *, 'size of ', bytes
      print *, 'size of int', sizeofint
      
C     Commit the datatype created 

      call MPI_TYPE_COMMIT(subrow, ierr) 

C     Create datatype for the sub-matrix 

      bytes = 20 * sizeofint
      call MPI_TYPE_HVECTOR(blocks, blocksize, bytes, subrow,
     &     submatrix, ierr) 

  
C     Commit the datatype created 

      call MPI_TYPE_COMMIT(submatrix, ierr) 
      call MPI_TYPE_SIZE(submatrix, bytes, ierr)
      print *, 'size of ', bytes

C     Send it to self and print it 

      numsend = 1
      numrecv = 25
      tag = 201
      call MPI_SENDRECV(a(1, 1), numsend, submatrix, rank, tag, 
     &     c(1, 1), numrecv, MPI_INTEGER, rank, 
     &     tag, MPI_COMM_WORLD, status, ierr) 
  
C     Print the submatrix 

      print *, 'a ', c(1, 1)
      print *, 'a ', c(1, 3)
      print *, 'a ', c(1, 5)

      if (rank .eq. 0) then
         do 30 i = 1, 5
            do 40 j = 1, 5
               print *, c(i, j)
 40         continue
 30      continue
      end if

      call MPI_FINALIZE(ierr)
      end