MPI_TYPE_CREATE_INDEXED_BLOCK(3)

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💖 MPI_Type_create_indexed_block 💖

(that's the page title btw — it lives in section 3 of the Open MPI manual, hiii)

🎀 NAME 🎀

MPI_Type_create_indexed_block, MPI_Type_create_hindexed_block — creates an indexed data type where literally every block is the same length. no cap. 💅

✨ SYNTAX ✨

🌸 C Syntax 🌸

#include <mpi.h>

int MPI_Type_create_indexed_block(int count, int blocklength, const int array_of_displacements[], MPI_Datatype oldtype, MPI_Datatype *newtype)

int MPI_Type_create_hindexed_block(int count, int blocklength, const MPI_Aint array_of_displacements[], MPI_Datatype oldtype, MPI_Datatype *newtype)

🌸 Fortran Syntax 🌸

USE MPI
! or the older form: INCLUDE 'mpif.h'
MPI_TYPE_CREATE_INDEXED_BLOCK(COUNT, BLOCKLENGTH,
             ARRAY_OF_DISPLACEMENTS, OLDTYPE, NEWTYPE, IERROR)
     INTEGER COUNT, BLOCKLENGTH, ARRAY_OF_DISPLACEMENTS(*),
             OLDTYPE, NEWTYPE, IERROR

MPI_TYPE_CREATE_HINDEXED_BLOCK(COUNT, BLOCKLENGTH,
             ARRAY_OF_DISPLACEMENTS, OLDTYPE, NEWTYPE, IERROR)
     INTEGER COUNT, BLOCKLENGTH, OLDTYPE, NEWTYPE
     INTEGER(KIND=MPI_ADDRESS_KIND) ARRAY_OF_DISPLACEMENTS(*)
     INTEGER IERROR

🌸 Fortran 2008 Syntax 🌸

USE mpi_f08
MPI_Type_create_indexed_block(count, blocklength, array_of_displacements,
             oldtype, newtype, ierror)
     INTEGER, INTENT(IN) :: count, blocklength,
     array_of_displacements(count)
     TYPE(MPI_Datatype), INTENT(IN) :: oldtype
     TYPE(MPI_Datatype), INTENT(OUT) :: newtype
     INTEGER, OPTIONAL, INTENT(OUT) :: ierror

MPI_Type_create_hindexed_block(count, blocklength, array_of_displacements,
             oldtype, newtype, ierror)
     INTEGER, INTENT(IN) :: count, blocklength
     INTEGER(KIND=MPI_ADDRESS_KIND), INTENT(IN) ::
     array_of_displacements(count)
     TYPE(MPI_Datatype), INTENT(IN) :: oldtype
     TYPE(MPI_Datatype), INTENT(OUT) :: newtype
     INTEGER, OPTIONAL, INTENT(OUT) :: ierror

🫶 INPUT PARAMETERS 🫶

  • count — length of array_of_displacements (an integer). like, how many entries you're handing over bestie 💜
  • blocklength — size of each block (integer). every block gets the exact same size, that's the whole ~thing~ ✨
  • array_of_displacements — array of displacements (array of integers). the units? it's giving depends on which function you called: in units of the extent of oldtype for MPI_Type_create_indexed_block, and in bytes for MPI_Type_create_hindexed_block. yes this distinction matters, don't skip it 🦋
  • oldtype — old data type (handle). the blueprint you're building on top of 👑

💅 OUTPUT PARAMETERS 💅

  • newtype — new data type (handle). shiny, fresh, yours 🌈
  • ierror — Fortran only: error status (integer). 📝

🌟 DESCRIPTION 🌟

So MPI_Type_create_indexed_block and MPI_Type_create_hindexed_block create an indexed data type where every single block has the same block length. iconic behaviour honestly. 🎀

The only difference between the two functions is this: MPI_Type_create_indexed_block takes an array of displacements measured in units of the extent of oldtype, while MPI_Type_create_hindexed_block takes displacements measured in bytes. that's it, that's the tea ☕

💀 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. fr fr. 😭

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. brutal but effective 💀
  • 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. lowkey surgical 🔥
  • MPI_ERRORS_RETURN — returns an error code to the application. the ✨chill✨ one 🫶

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. like, it might just be over. 😭 no cap.

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_Type_indexed

2003-2026, The Open MPI Community 🫶

okay bestie that's the whole page, you're officially fluent in indexed block types now, go slay ✨💖🦋

MPI_TYPE_CREATE_INDEXED_BLOCK(3) — Open MPI — this lil masterpiece dropped Sep 10, 2026 and no, I will not be taking questions about how the date is in the future, time is fake, the docs are eternal 🌈⭐

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