Data types

One argument that usually must be given to MPI routines is the type of the data being passed. User-defined datatypes (an advanced MPI topic) allows MPI to automatically scatter and gather data to and from non-contiguous buffers. MPI defines a number of constants that correspond to language datatypes in Fortran and C.

When an MPI routine is called, the Fortran data type of the data being passed must match the corresponding MPI integer constant. The following table the MPI 1.2 datatype definitions.

Type 			Length
--------------- 	------
MPI_PACKED 		1
MPI_BYTE 		1
MPI_CHAR 		1
MPI_UNSIGNED_CHAR 	1
MPI_SIGNED_CHAR 	1
MPI_WCHAR 		2
MPI_SHORT 		2
MPI_UNSIGNED_SHORT 	2
MPI_INT 		4
MPI_UNSIGNED 		4
MPI_LONG 		4
MPI_UNSIGNED_LONG 	4
MPI_FLOAT 		4
MPI_DOUBLE 		8
MPI_LONG_DOUBLE 	16
MPI_CHARACTER 		1
MPI_LOGICAL 		4
MPI_INTEGER 		4
MPI_REAL 		4
MPI_DOUBLE_PRECISION 	8
MPI_COMPLEX 		2*4
MPI_DOUBLE_COMPLEX 	2*8

Optional Type 		Length
------------------ 	------
MPI_INTEGER1 		1
MPI_INTEGER2 		2
MPI_INTEGER4 		4
MPI_INTEGER8 		8
MPI_LONG_LONG 		8
MPI_UNSIGNED_LONG_LONG 	8
MPI_REAL4 		4
MPI_REAL8 		8
MPI_REAL16 		16