NAME

       MPI_Type_create_f90_real - Returns a bounded MPI real datatype

SYNTAX

C Syntax

       #include <mpi.h>
       int MPI_Type_create_f90_real(int p, int r, MPI_Datatype *newtype)

Fortran Syntax

       USE MPI
       ! or the older form: INCLUDE 'mpif.h'
       MPI_TYPE_CREATE_F90_REAL (P, R, NEWTYPE, IERROR)
            INTEGER   P, R, NEWTYPE, IERROR

Fortran 2008 Syntax

       USE mpi_f08
       MPI_Type_create_f90_real(p, r, newtype, ierror)
            INTEGER, INTENT(IN) :: p, r
            TYPE(MPI_Datatype), INTENT(OUT) :: newtype
            INTEGER, OPTIONAL, INTENT(OUT) :: ierror

C++ Syntax

       #include <mpi.h>
       static MPI::Datatype MPI::Datatype::Create_f90_real(int p, int r)

INPUT PARAMETERS

       p         Precision, in decimal digits (integer).

       r         Decimal exponent range (integer).

OUTPUT PARAMETERS

       newtype   New data type (handle).

       IERROR    Fortran only: Error status (integer).

DESCRIPTION

       This  function  provides  a  way  to  declare  KIND-parameterized  REAL  MPI datatypes. The arguments are
       interpreted in a similar fashion to the F90 function SELECTED_REAL_KIND. The parameters p and r  must  be
       scalar  integers. The argument p represents the required level of numerical precision, in decimal digits.
       The r parameter indicates the range of exponents desired: the returned datatype will have  at  least  one
       exponent between +r and -r (inclusive).

       Either  p or r, but not both, may be omitted from calls to SELECTED_REAL_KIND. Similarly, either argument
       to MPI_Type_create_f90_real may be set to MPI_UNDEFINED.

NOTES

       It is erroneous to supply values for p and r not supported by the compiler.

       The Fortran function SELECTED_REAL_KIND maps a large number of (p,r) pairs 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  (p,r)  arguments  to
       SELECTED_REAL_KIND.  However,  to  help  facilitate  interoperability  in  a  heterogeneous  environment,
       equivalency  is  more  strictly  defined  for  datatypes  returned  by  MPI_Type_create_f90_real. Two MPI
       datatypes, each generated by this function, will match if and only if they have identical values for both
       p and 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 (p > 33) and/or (r > 4931):
                 external32 size = n/a (undefined)
            else if (p > 15) and/or (r > 307):
                 external32 size = 16
            else if (p > 6) and/or (r > 37):
                 external32 size = 8
            else:
                 external32 size = 4

       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_REAL_KIND (i.e., p and/or r are 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.

SEE ALSO

       MPI_Pack_external
       MPI_Sizeof
       MPI_Type_match_size
       MPI_Unpack_external
       SELECTED_REAL_KIND