Note the code in the example
/* Open viewer for binary output */ ierr = PetscViewerBinaryOpen(PETSC_COMM_SELF,"input.dat",FILE_MODE_WRITE,&view_out);CHKERRQ(ierr); ierr = PetscViewerBinaryGetDescriptor(view_out,&fd);CHKERRQ(ierr); /* Write binary output */ ierr = PetscBinaryWrite(fd,&m,1,PETSC_INT,PETSC_FALSE);CHKERRQ(ierr); ierr = PetscBinaryWrite(fd,array,m,PETSC_SCALAR,PETSC_FALSE);CHKERRQ(ierr); this means each process is opening the same file for writing (because the argument to PetscViewerBinaryOpen() is PETSC_COMM_SELF) and then all of the processes are writing to this same file (completely uncoordinated). In general this won't work, it will just make a mess of things. This is why this example has the line > if (size != 1) SETERRQ(PETSC_COMM_SELF,1,"This is a uniprocessor example > only!"); Barry > On Nov 17, 2018, at 1:12 PM, Fazlul Huq via petsc-users > <petsc-users@mcs.anl.gov> wrote: > > Hello PETSc developers, > > In example 6 or vec section I don't understand this line: > if (size != 1) SETERRQ(PETSC_COMM_SELF,1,"This is a uniprocessor example > only!"); > > I tried to run the code with "mpiexec -n 2 ./ex6" or "mpiexec -n 4 ./ex6" or > even "mpiexec -n 1 ./ex6" it the code runs properly. > > Thanks. > > Sincerely, > Huq > > -- > > Fazlul Huq > Graduate Research Assistant > Department of Nuclear, Plasma & Radiological Engineering (NPRE) > University of Illinois at Urbana-Champaign (UIUC) > E-mail: huq2...@gmail.com
