[petsc-users] Output question for ex29.

[Matthew Knepley]

On Fri, Jun 10, 2011 at 3:16 PM, Alan Wei <zhenglun.wei at gmail.com> wrote:

> ooops, sorry, here it is.
>

You did not pass a valid communicator to PetscVIewerASCIIOpen(). Use
PETSC_COMM_WORLD.

   Matt


> ^_^
>
> Alan
>
>
> On Fri, Jun 10, 2011 at 3:09 PM, Matthew Knepley <knepley at gmail.com>wrote:
>
>> On Fri, Jun 10, 2011 at 3:05 PM, <zhenglun.wei at gmail.com> wrote:
>>
>>> 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);
>>>
>>
>> I told you to use ASCII_VTK, not 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.
>>>
>>
>> How can I possibly know what went wrong if you do not send the ENTIRE
>> error message.
>>
>>    Matt
>>
>>
>>> 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
>>> >
>>>
>>
>>
>>
>> --
>> 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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