MPI_TYPE_CREATE_F90_REAL(3)

MPI_TYPE_CREATE_F90_REAL(3) 💖

okay so bestie, welcome to the Open MPI manual page for MPI_Type_create_f90_real — it returns a bounded MPI real datatype. This is your little guide to KIND-parameterized REAL MPI datatypes, and yes, it’s giving “niche but iconic.” ✨

✨ 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

🌸 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 💖

okay so here’s the tea: this function gives you 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. no cap.

🦋 NOTES 🦋

🚨 it is erroneous to supply values for p and r not supported by the compiler. Like, bestie, don’t do that. 🙈

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 return result of the function and Fortran routines in the last argument. 💅

Before the error value is returned, the current MPI error handler associated with the communication object (e.g., communicator, window, file) is called. If no communication object is associated with the MPI call, then the call is considered attached to MPI_COMM_SELF and will call the associated MPI error handler. When MPI_COMM_SELF is not initialized (i.e., before MPI_Init/MPI_Init_thread, after MPI_Finalize, or when using the Sessions Model exclusively) the error raises the initial error handler. The initial error handler can be changed by calling MPI_Comm_set_errhandler on MPI_COMM_SELF when using the World model, or the mpi_initial_errhandler CLI argument to mpiexec or info key to MPI_Comm_spawn/MPI_Comm_spawn_multiple. If no other appropriate error handler has been set, then the MPI_ERRORS_RETURN error handler is called for MPI I/O functions and the MPI_ERRORS_ABORT error handler is called for all other MPI functions. 🔥

Open MPI includes three predefined error handlers that can be used:

• MPI_ERRORS_ARE_FATAL — Causes the program to abort all connected MPI processes. 💀
• MPI_ERRORS_ABORT — An error handler that can be invoked on a communicator, window, file, or session. When called on a communicator, it acts as if MPI_Abort was called on that communicator. If called on a window or file, acts as if MPI_Abort was called on a communicator containing the group of processes in the corresponding window or file. If called on a session, aborts only the local process. 😭
• MPI_ERRORS_RETURN — Returns an error code to the application. 🫶

MPI applications can also implement their own error handlers by calling:

• MPI_Comm_create_errhandler then MPI_Comm_set_errhandler
• MPI_File_create_errhandler then MPI_File_set_errhandler
• MPI_Session_create_errhandler then MPI_Session_set_errhandler or at MPI_Session_init
• MPI_Win_create_errhandler then MPI_Win_set_errhandler

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 the Error Handling section of the MPI-3.1 standard for more information. 📚

👀 SEE ALSO 👀

• MPI_Pack_external
• MPI_Sizeof
• MPI_Type_match_size
• MPI_Unpack_external
• SELECTED_REAL_KIND

🎀 COPYRIGHT 🎀

2003-2026, The Open MPI Community

xoxo, Open MPI 💖 — page dated Sep 11, 2026 ✨