I think you are asking if you have
A00 A01
0 A11
Can you use field split trivially to solve this upper block triangular system
by doing "backward/reverse" block Gauss-Seidel?
The very short answer is no
1) you can use -pc_fieldsplit_type symmetric_multiplicative but then it does
the A00 solve twice unnecessarily
2) what Matt is saying you can define you 00 index set to be associated with
the second block A11 then that flips the block rows and columns of the matrix
and
the regular multiplicative field split will work like the backward block
GS on the original matrix.
Barry
Yes, we could add something like -pc_fieldsplit_type backward_multiplicative
but as Matt points out that is not strictly needed.
On Aug 20, 2012, at 7:18 AM, Thomas Witkowski <thomas.witkowski at
tu-dresden.de> wrote:
> Am 20.08.2012 13:39, schrieb Matthew Knepley:
>> On Mon, Aug 20, 2012 at 3:09 AM, Thomas Witkowski <thomas.witkowski at
>> tu-dresden.de> wrote:
>> Is it possible to change the PCFIELDSPLIT / block Gauss-Seidel
>> preconditioner to use A_01 instead of A_10 to solve an upper triangular
>> system?
>>
>> It always uses A_01. What exactly do you want to do?
> In this case the documentation should be changed (see p. 86)
>
> Thomas
>
>>
>> Matt
>>
>>
>> Thomas
>>
>>
>>
>> --
>> 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
>
