how do you access the nonzero elements in SeqAIJ matrices

[Barry Smith]

    Send us the code. This is suppose to be easy stuff.

    Barry

On Aug 4, 2008, at 11:09 AM, Ahmed El Zein wrote:

> On Mon, 2008-08-04 at 23:13 +0800, Zi-Hao Wei wrote:
>> On Mon, Aug 4, 2008 at 10:53 PM, Ahmed El Zein <ahmed at azein.com>  
>> wrote:
>>> my code looks like:
>>>   ierr = MatCreate(PETSC_COMM_WORLD,&A); CHKERRQ(ierr);
>>>   ierr = MatSetSizes(A,M,N,M,N); CHKERRQ(ierr);
>>>   ierr = MatSetType(A, MATSEQAIJ); CHKERRQ(ierr);
>>>   ierr =  MatAssemblyBegin(A, MAT_FINAL_ASSEMBLY); CHKERRQ(ierr);
>>>   [...lots of MatSetValue() calls...]
>>>   ierr = MatAssemblyEnd(A, MAT_FINAL_ASSEMBLY); CHKERRQ(ierr);
>>
>> I think that the code should be
>>  ierr = MatCreate(PETSC_COMM_WORLD,&A); CHKERRQ(ierr);
>>  ierr = MatSetSizes(A,M,N,M,N); CHKERRQ(ierr);
>>  ierr = MatSetType(A, MATSEQAIJ); CHKERRQ(ierr);
>>  [...lots of MatSetValue() calls...]
>>  ierr = MatAssemblyBegin(A, MAT_FINAL_ASSEMBLY); CHKERRQ(ierr);
>>  ierr = MatAssemblyEnd(A, MAT_FINAL_ASSEMBLY); CHKERRQ(ierr);
>>
>> The routines MatAssemblyBegin and MatAssemblyEnd should be called
>> after completing all calls to MatSetValues().
> You are right of course. But if these 2 calls are meant to be right
> after each other, why isn't there just one MatAssembly() call versus a
> Begin and End call?
>
> btw fixing this did not affect the problem I had.
>
> Ahmed
>