MPI_TYPE_LB(3)					     Open MPI					    MPI_TYPE_LB(3)

MPI_Type_lb  — Returns the lower bound of a data type — this routine is deprecated in favor of MPI_Type_get_extent
<#mpi-type-get-extent>.

SYNTAX
   C Syntax
	  #include <mpi.h>

	  int MPI_Type_lb(MPI_Datatype datatype, MPI_Aint *displacement)

   Fortran Syntax
	  USE MPI
	  ! or the older form: INCLUDE 'mpif.h'

	  MPI_TYPE_LB(DATATYPE, DISPLACEMENT, IERROR)
	       INTEGER DATATYPE, DISPLACEMENT, IERROR

INPUT PARAMETER
       • datatype: Datatype (handle).

OUTPUT PARAMETERS
       • displacement: Displacement of lower bound from origin, in bytes (integer).

       • ierror: Fortran only: Error status (integer).

DESCRIPTION
       Note  that  use	of  this  routine  is  deprecated  as  of  MPI-2.  Please   use	  MPI_Type_get_extent	<#
       mpi-type-get-extent> instead.

       MPI_Type_lb  returns  the lower bound of a data type. This may differ from zero if the type was constructed
       using MPI_LB.

       The “pseudo-datatypes,” MPI_LB and MPI_UB, can be used, respectively, to mark the lower bound (or the upper
       bound) of a datatype. These pseudo-datatypes occupy no space (extent (MPI_LB) = extent (MPI_UB)	=0.   They
       do not affect the size or count of a datatype, and do not affect the context of a message created with this
       datatype.  However,  they  do  affect the definition of the extent of a datatype and, therefore, affect the
       outcome of a replication of this datatype by a datatype constructor.

       In general, if

	  Typemap = {(type0, disp0), ..., (type(n-1), disp(n-1)}

       then the lower bound of Typemap is defined to be

			(min(j) disp(j)				 if no entry has
	  lb(Typemap) = (					 basic type lb
			(min(j) {disp(j) such that type(j) = lb} otherwise

       Similarly, the upper bound of Typemap is defined to be

			    (max(j) disp(j) + sizeof((type(j)) + e   if no entry has
	      ub(Typemap) = (					     basic type ub
			    (max(j) {disp(j) such that type(j) = ub} otherwise

	  Then

	      extent(Typemap) = ub(Typemap) - lb(Typemap)

       If type(i) requires alignment to a byte address that is a multiple of k(i), then e is the least nonnegative
       increment needed to round extent(Typemap) to the next multiple of max(i) k(i).

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>/MPI_Init_thread  <#mpi-init-thread>,
       after  MPI_Finalize  <#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	<#
       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>/MPI_Comm_spawn_multiple	<#
       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 <#mpi-abort> was called on that communicator. If called
	 on a window or file, acts as if MPI_Abort <#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	 <#mpi-comm-create-errhandler>	   then	    MPI_Comm_set_errhandler	<#
	 mpi-comm-set-errhandler>

       • MPI_File_create_errhandler	<#mpi-file-create-errhandler>	  then	   MPI_File_set_errhandler	<#
	 mpi-file-set-errhandler>

       • MPI_Session_create_errhandler	 <#mpi-session-create-errhandler>   then   MPI_Session_set_errhandler	<#
	 mpi-session-set-errhandler> or at MPI_Session_init <#mpi-session-init>

       • MPI_Win_create_errhandler	<#mpi-win-create-errhandler>	  then	    MPI_Win_set_errhandler	<#
	 mpi-win-set-errhandler>

       Note that MPI does not guarantee that an MPI program can continue past an error.

       See the MPI man page <#open-mpi> for a full list of MPI error codes <#open-mpi-errors>.

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

       See also:

	  • MPI_Type_get_extent <#mpi-type-get-extent>

Copyright
       2003-2026, The Open MPI Community

						   Mar 05, 2026					    MPI_TYPE_LB(3)
