[petsc-users] MatZeroRowsColumns

[Matthew Knepley]

On Fri, Nov 24, 2017 at 6:42 AM, Samuel Lanthaler <s.lanthaler at gmail.com>
wrote:

> Ah, great. I didn't understand that "optional" arguments are not optional
> in the fortran sense of the word. After setting up two vectors to pass to
> the routine, the program works. Thank you very much!
>
> One additional question: In the documentation, it is written that I can
> pass PETSC_NULL for these two vectors, if I don't actually need them. That
> probably only works in C, but not in fortran. Is there a corresponding
> argument I can pass to the routine in fortran? It seems, that
> PETSC_NULL_REAL doesn't work; is there some other PETSC_NULL_XXX that
> should be passed in this case from fortran? If not, then I'll just stick to
> creating vectors and distroying them afterwards, which is fine for me as
> well.
>

You can use PETSC_NULL_VEC

  Thanks,

     Matt


> Cheers,
> Sam
>
>
> On 11/24/2017 01:56 AM, Smith, Barry F. wrote:
>
>> MatZeroRowsColumns() as two vector arguments you are missing
>>
>>
>> On Nov 23, 2017, at 2:43 PM, Samuel Lanthaler <s.lanthaler at gmail.com>
>>> wrote:
>>>
>>> Hi there,
>>> I'm new to PETSc and have been trying to do some basic manipulation of
>>> matrices in fortran, but don't seem to be able to set a row/column to zero
>>> using the MatZeroRowsColumns command: The following is a small example
>>> program:
>>>
>>> ! initialize PETSc
>>>    CALL PetscInitialize(PETSC_NULL_CHARACTER,ierr)
>>>
>>>    ! Set up a new matrix
>>>    m = 3
>>>    CALL MatCreate(PETSC_COMM_WORLD,matA,ierr); CHKERRQ(ierr);
>>>    CALL MatSetType(matA,MATMPIAIJ,ierr); CHKERRQ(ierr);
>>>    CALL MatSetSizes(matA,PETSC_DECIDE,PETSC_DECIDE,m,m,ierr);
>>> CHKERRQ(ierr);
>>>    CALL MatMPIAIJSetPreallocation(matA,3,PETSC_NULL_INTEGER,3,PETSC_NULL_INTEGER,ierr);
>>> CHKERRQ(ierr);
>>>
>>>    ! set values of matrix
>>>    vals(1,:) = (/1.,2.,3./)
>>>    vals(2,:) = (/4.,5.,6./)
>>>    vals(3,:) = (/7.,8.,9./)
>>>    !
>>>    idxm = (/0,1,2/)
>>>    idxn = (/0,1,2/)
>>>    !
>>>    CALL MatSetValues(matA,3,idxm,3,idxn,vals,INSERT_VALUES,ierr);
>>> CHKERRQ(ierr);
>>>       ! assemble matrix
>>>    CALL MatAssemblyBegin(matA,MAT_FINAL_ASSEMBLY,ierr); CHKERRQ(ierr);
>>>    CALL MatAssemblyEnd(matA,MAT_FINAL_ASSEMBLY,ierr); CHKERRQ(ierr);
>>>      ! set one row/column to zero, put 6.0d0 on diagonal
>>>    idone(1) = 2
>>>    val = 6.0d0
>>>    CALL MatZeroRowsColumns(matA,1,idone,val,ierr); CHKERRQ(ierr);
>>>
>>> ! finalize PETSc
>>>    CALL PetscFinalize(PETSC_NULL_CHARACTER,ierr)
>>>
>>> When running the program, I get the following error message:
>>>
>>> [0]PETSC ERROR: ------------------------------
>>> ------------------------------------------
>>> [0]PETSC ERROR: Caught signal number 11 SEGV: Segmentation Violation,
>>> probably memory access out of range
>>> [0]PETSC ERROR: Try option -start_in_debugger or
>>> -on_error_attach_debugger
>>> [0]PETSC ERROR: or see http://www.mcs.anl.gov/petsc/d
>>> ocumentation/faq.html#valgrind
>>> [0]PETSC ERROR: or try http://valgrind.org on GNU/linux and Apple Mac
>>> OS X to find memory corruption errors
>>> [0]PETSC ERROR: likely location of problem given in stack below
>>> [0]PETSC ERROR: ---------------------  Stack Frames
>>> ------------------------------------
>>> [0]PETSC ERROR: Note: The EXACT line numbers in the stack are not
>>> available,
>>> [0]PETSC ERROR:       INSTEAD the line number of the start of the
>>> function
>>> [0]PETSC ERROR:       is given.
>>> [0]PETSC ERROR: --------------------- Error Message
>>> --------------------------------------------------------------
>>> [0]PETSC ERROR: Signal received
>>> [0]PETSC ERROR: See http://www.mcs.anl.gov/petsc/documentation/faq.html
>>> for trouble shooting.
>>> [0]PETSC ERROR: Petsc Release Version 3.8.2, Nov, 09, 2017
>>> [0]PETSC ERROR: ./test on a arch-complex-debug named sam-ThinkPad-T450s
>>> by sam Thu Nov 23 23:28:15 2017
>>> [0]PETSC ERROR: Configure options PETSC_DIR=/home/sam/Progs/petsc-3.8.2
>>> PETSC_ARCH=arch-complex-debug --with-scalar-type=complex
>>> [0]PETSC ERROR: #1 User provided function() line 0 in  unknown file
>>> ------------------------------------------------------------
>>> --------------
>>> MPI_ABORT was invoked on rank 0 in communicator MPI_COMM_WORLD
>>> with errorcode 59.
>>> Would someone be so kind as to tell me what I'm doing wrong? Thank you!
>>>
>>> Best regards,
>>> Sam
>>>
>>
>


-- 
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

https://www.cse.buffalo.edu/~knepley/ <http://www.caam.rice.edu/~mk51/>
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