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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

       INCLUDE 'mpif.h'
       MPI_TYPE_CREATE_F90_REAL (P, R, NEWTYPE, IERROR)
            INTEGER   P, R, NEWTYPE, 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



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