MPI_Type_create_f90_real(3) Open MPI MPI_Type_create_f90_real(3)NAMEMPI_Type_create_f90_real - Returns a bounded MPI real datatype
SYNTAXC 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 expo‐
nent 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_cre‐
ate_f90_real may be set to MPI_UNDEFINED.
NOTES
It is erroneous to supply values for p and r not supported by the com‐
piler.
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 com‐
piler. 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 parame‐
ters were generated by different (p,r) arguments to SELECTED_REAL_KIND.
However, to help facilitate interoperability in a heterogeneous envi‐
ronment, 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 exter‐
nal32 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 exter‐
nal32 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++ func‐
tions 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
1.6.4 Feb 19, 2013 MPI_Type_create_f90_real(3)
