Ubuntu Manpage: MPI_Type_create_f90_integer - Returns a bounded MPI integer datatype

Provided by: openmpi-doc_4.1.6-7ubuntu2_all

NAME

       MPI_Type_create_f90_integer - Returns a bounded MPI integer datatype

SYNTAX

C Syntax

       #include <mpi.h>
       int MPI_Type_create_f90_integer(int r, MPI_Datatype *newtype)

Fortran Syntax

       USE MPI
       ! or the older form: INCLUDE 'mpif.h'
       MPI_TYPE_CREATE_F90_INTEGER (R, NEWTYPE, IERROR)
            INTEGER   R, NEWTYPE, IERROR

Fortran 2008 Syntax

       USE mpi_f08
       MPI_Type_create_f90_integer(r, newtype, ierror)
            INTEGER, INTENT(IN) :: r
            TYPE(MPI_Datatype), INTENT(OUT) :: newtype
            INTEGER, OPTIONAL, INTENT(OUT) :: ierror

C++ Syntax

       #include <mpi.h>
       static MPI::Datatype MPI::Datatype::Create_f90_integer(int r)

INPUT PARAMETER

       r         Precision, in decimal digits (integer).

OUTPUT PARAMETERS

       newtype   New data type (handle).

       IERROR    Fortran only: Error status (integer).

DESCRIPTION

       This  function  provides  a  way  to declare KIND-parameterized INTEGER MPI datatypes. The
       argument is interpreted in a similar fashion to the F90 function SELECTED_INT_KIND: r must
       be  a  scalar integer, and represents the desired level of numerical precision, in decimal
       digits.

NOTES

It is erroneous to supply a value for r not supported by the compiler.

The Fortran function SELECTED_INT_KIND maps a large number of r values to a much smaller
number of KIND parameters supported by the compiler. KIND parameters are not specified by
the language and are not portable. From the point of view of the language, variables of
the same base type and KIND parameter are equivalent, even if their KIND parameters were
generated by different r arguments to SELECTED_INT_KIND. However, to help facilitate
interoperability in a heterogeneous environment, equivalency is more strictly defined for
datatypes returned by MPI_Type_create_f90_integer. Two MPI datatypes, each generated by
this function, will match if and only if they have identical values for r.

The interaction between the datatypes returned by this function and the external32 data
representation - used by MPI_Pack_external, MPI_Unpack_external and many MPI_File
functions - is subtle. The external32 representation of returned datatypes is as follows.

if (r > 38):
external32 size = n/a (undefined)
else if (r > 18):
external32 size = 16
else if (r > 9):
external32 size = 8
else if (r > 4):
external32 size = 4
else if (r > 2):
external32 size = 2
else:
external32 size = 1

If the external32 representation of a datatype is undefined, so are the results of using
that datatype in operations that require the external32 format. Care should be taken not
to use incompatible datatypes indirectly, e.g., as part of another datatype or through a
duplicated datatype, in these functions.

If a variable is declared specifying a nondefault KIND value that was not obtained with
SELECTED_INT_KIND (i.e., r is unknown), the only way to obtain a matching MPI datatype is
to use the functions MPI_Sizeof and MPI_Type_match_size.

ERRORS

       Almost all MPI routines return an error value; C routines as the value of the function and
       Fortran  routines in the last argument. C++ functions do not return errors. If the default
       error handler is set to MPI::ERRORS_THROW_EXCEPTIONS, then  on  error  the  C++  exception
       mechanism will be used to throw an MPI::Exception object.

       Before  the  error value is returned, the current MPI error handler is called. By default,
       this error handler aborts the MPI job, except for I/O function errors. The  error  handler
       may    be   changed   with   MPI_Comm_set_errhandler;   the   predefined   error   handler
       MPI_ERRORS_RETURN may be used to cause error values to be returned. Note that MPI does not
       guarantee that an MPI program can continue past an error.

       See the MPI man page for a full list of MPI error codes.