petsc-3.7.3 2016-07-24
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# PetscSequentialPhaseBegin

Begins a sequential section of code.

### Synopsis

    #include "petscsys.h"
    PetscErrorCode  PetscSequentialPhaseBegin(MPI_Comm comm,int ng)

Collective on MPI_Comm

### Input Parameters

| comm | - Communicator to sequentialize.
| ng | - Number in processor group. This many processes are allowed to execute at the same time (usually 1)

### Notes

PetscSequentialPhaseBegin() and PetscSequentialPhaseEnd() provide a way to force a section of code to be executed by the processes in rank order. Typically, this is done with

          PetscSequentialPhaseBegin(comm, 1);
          <code to be executed sequentially>
          PetscSequentialPhaseEnd(comm, 1);

Often, the sequential code contains output statements (e.g., printf) to be executed. Note that you may need to flush the I/O buffers before calling PetscSequentialPhaseEnd(). Also, note that some systems do not propagate I/O in any order to the controling terminal (in other words, even if you flush the output, you may not get the data in the order that you want).

### See Also

PetscSequentialPhaseEnd()

Level:intermediate
Location: src/sys/utils/mpiu.c
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