[petsc-users] Output question for ex29.

[zhenglun.wei at gmail.com]

Dear Matt,
Following your suggestions, I modified the VecView_VTK in  
/src/ksp/ksp/example/tutorial/ex29.c to

PetscFunctionBegin;
PetscViewerASCIIOpen(comm, filename, &viewer);
PetscViewerSetFormat(viewer, PETSC_VIEWER_ASCII_MATLAB);
DMView(x, viewer);
VecView(x, PETSC_VIEWER_STDOUT_WORLD);
PetscViewerDestroy(&viewer);
PetscFunctionReturn(0);

However, I always give me some error. Could you please briefly check if  
there is any obvious coding problem here.

thanks,
Alan

On , Matthew Knepley <knepley at gmail.com> wrote:
> On Thu, Jun 9, 2011 at 6:18 PM, Matthew Knepley knepley at gmail.com> wrote:

> On Thu, Jun 9, 2011 at 6:01 PM, zhenglun.wei at gmail.com> wrote:


> Dear Sir/Madam,
> I'm still studying on the ex29 of /src/ksp/ksp/example/tutorial. Before I  
> met a problem on VecView_VTK in parallel computation. I'm trying to  
> modify it in order to output some data from the computation.




> Here is a better answer. If you want output, throw away this old function  
> which is broken, and use


> PetscViewerASCIIOpen()
> PetscViewerASCIISetFormat(PETSC_VIEWER_ASCII_VTK)

> DMView()
> VecView()
> PetscViewerDestroy()


> Thanks,


> Matt


> 1) My first questions is that what does this section do in VecView_VTK:

> 272: MPI_Comm_rank(comm, &rank);

> 273: MPI_Comm_size(comm, &size);
> 274: MPI_Reduce(&n, &maxn, 1, MPIU_INT, MPI_MAX, 0, comm);

> 275: tag = ((PetscObject) viewer)->tag;
> 276: if (!rank) {
> 277: PetscMalloc((maxn+1) * sizeof(PetscScalar), &values);
> 278: for(i = 0; i 279: PetscViewerASCIIPrintf(viewer, "%G\n",  
> PetscRealPart(array[i]));


> 280: }
> 281: for(p = 1; p 282: MPI_Recv(values, (PetscMPIInt) n, MPIU_SCALAR, p,  
> tag, comm, &status);
> 283: MPI_Get_count(&status, MPIU_SCALAR, &nn);
> 284: for(i = 0; i

> 285: PetscViewerASCIIPrintf(viewer, "%G\n", PetscRealPart(array[i]));
> 286: }
> 287: }
> 288: PetscFree(values);
> 289: } else {
> 290: MPI_Send(array, n, MPIU_SCALAR, 0, tag, comm);


> 291: }

> What I understand is: it gather all the data from different process in  
> parallel computation, and output it to the 'viewer'. I comment out  
> everything in VecView_VTK except this part, there is no error message  
> coming up in my parallel computation so far.



> 2) however, I really don't know how did it split the domain for parallel  
> computation. For example, if I use 4 processes, is the domain split like:


> The DMDA describes the domain splitting.




> Matt

> a)
> |
> 0 | 1
> |


> ---------------|--------------
> |
> 2 | 3
> |

> b)
> |
> 0 | 2
> |
> ---------------|--------------
> |


> 1 | 3
> |

> c)
> | | | |
> | | | |
> 0 | | 2 | |
> | 1 | | 3 |
> | | | |
> | | | |



> d)
> 0
> ------------------------
> 1
> ------------------------
> 2
> ------------------------
> 3

> thanks in advance,
> Alan




> --
> What most experimenters take for granted before they begin their  
> experiments is infinitely more interesting than any results to which  
> their experiments lead.
> -- Norbert Wiener




> --
> What most experimenters take for granted before they begin their  
> experiments is infinitely more interesting than any results to which  
> their experiments lead.
> -- Norbert Wiener

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