03-19-2009
Help required to understand a variable in shell script!!!
Hi,
I need to understand the following script:
a=`dirname $0`
b=`uname -s`
if [ "${a:0:1}" = "/" ] ; then
c=$a/../../../platforms/$b/extlib
else
c=`pwd`/$a/../../../platforms/$b/extlib
fi
There are a bunch of variable assignments going on here!!!
What does this variable means: "${a:0:1}"
Thanks!!!
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LEARN ABOUT OSX
mpi_alloc_mem
MPI_Alloc_mem(3OpenMPI) MPI_Alloc_mem(3OpenMPI)
NAME
MPI_Alloc_mem - Allocates a specified memory segment.
SYNTAX
C Syntax
#include <mpi.h>
int MPI_Alloc_mem(MPI_Aint size, MPI_Info info, void *baseptr)
Fortran Syntax (see FORTRAN NOTES)
INCLUDE 'mpif.h'
MPI_ALLOC_MEM(SIZE, INFO, BASEPTR, IERROR)
INTEGER INFO, IERROR
INTEGER(KIND=MPI_ADDRESS_KIND) SIZE, BASEPTR
C++ Syntax
#include <mpi.h>
void* MPI::Alloc_mem(MPI::Aint size, const MPI::Info& info)
INPUT PARAMETERS
size Size of memory segment in bytes (nonnegative integer).
info Info argument (handle).
OUTPUT PARAMETERS
baseptr Pointer to beginning of memory segment allocated.
IERROR Fortran only: Error status (integer).
DESCRIPTION
MPI_Alloc_mem allocates size bytes of memory. The starting address of this memory is returned in the variable base.
FORTRAN NOTES
There is no portable FORTRAN 77 syntax for using MPI_Alloc_mem. There is no portable Fortran syntax for using pointers returned from
MPI_Alloc_mem. However, MPI_Alloc_mem can be used with Sun Fortran compilers.
From FORTRAN 77, you can use the following non-standard declarations for the SIZE and BASEPTR arguments:
INCLUDE "mpif.h"
INTEGER*MPI_ADDRESS_KIND SIZE, BASEPTR
From either FORTRAN 77 or Fortran 90, you can use "Cray pointers" for the BASEPTR argument. Cray pointers are described further in the For-
tran User's Guide and are supported by many Fortran compilers. For example,
INCLUDE "mpif.h"
REAL*4 A(100,100)
POINTER (BASEPTR, A)
INTEGER*MPI_ADDRESS_KIND SIZE
SIZE = 4 * 100 * 100
CALL MPI_ALLOC_MEM(SIZE,MPI_INFO_NULL,BASEPTR,IERR)
! use A
CALL MPI_FREE_MEM(A, IERR)
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 ALSO
MPI_Free_mem
Open MPI 1.2 September 2006 MPI_Alloc_mem(3OpenMPI)