[petsc-users] PCComposite

[Hui Zhang]

On May 28, 2012, at 5:16 PM, Jed Brown wrote:

> On Mon, May 28, 2012 at 9:40 AM, Hui Zhang <mike.hui.zhang at hotmail.com> wrote:
> 
> On May 28, 2012, at 3:42 PM, Jed Brown wrote:
> 
>> On Mon, May 28, 2012 at 8:40 AM, Hui Zhang <mike.hui.zhang at hotmail.com> wrote:
>> 
>> On May 28, 2012, at 3:20 PM, Jed Brown wrote:
>> 
>>> On Mon, May 28, 2012 at 5:19 AM, Hui Zhang <mike.hui.zhang at hotmail.com> wrote:
>>> Sorry for repost the following question, but after reading composite.c and asm.c,
>>> I can not understand.  I observed that my subroutine for modifying submatrices of PCASM was
>>> called twice.  In composite.c it seems there is no calling of PCSetUp on its componential PC's.
>>> In asm.c, the PCSetUp_ASM first determines whether pc->setupcalled is true.
>>> 
>>> I think this is a general question for PCComposite say pc. If it consists of two pc's  pc0, pc1
>>> and I have PCSetUp(pc0), I would not expect pc0 to be SetUp again.  I can not understand
>>> in my case why PCASM seems SetUp twice.
>>> 
>>> Does the routine do anything or just return immediately? If nothing has been changed since the last time a PC was set up, it should return immediately. If you have changed some configuration, it may need to be set up again.
>> 
>> Thanks. But I said something wrong.  The source code asm.c does call the ModifySubMatrices
>> whenever PCSetUp is called on PCASM, no matter whether it was called before.  So this 
>> explains my observation (two calls of ModifySubMatrices).  My new question is:  can you
>> add a user control to determine whether MatGetSubMatrices and PCModifySubMatrices 
>> should be called inside PCSetUp_ASM ?  But maybe this is too invasive and not
>> very useful to most people (although useful to me).
>> 
>> It does not reach PCSetUp_ASM unless something has changed. Run with -info and/or in a debugger to see why.
>> 
>> PetscErrorCode  PCSetUp(PC pc)
>> {
>>   PetscErrorCode ierr;
>>   const char     *def;
>> 
>>   PetscFunctionBegin;
>>   PetscValidHeaderSpecific(pc,PC_CLASSID,1);
>>   if (!pc->mat) SETERRQ(((PetscObject)pc)->comm,PETSC_ERR_ARG_WRONGSTATE,"Matrix must be set first");
>> 
>>   if (pc->setupcalled > 1) {
>>     ierr = PetscInfo(pc,"Setting PC with identical preconditioner\n");CHKERRQ(ierr);
>>     PetscFunctionReturn(0);
>> 
> 
> 
> Thanks for the hints.  I found why (I hope).  We have KSP named ksp and its PC is pc,
> and pc is PCComposite with pc0, pc1. The program runs like KSPSetUp on ksp, which
> calls PCSetUp on pc, i.e. PCSetUp_Composite on pc.  The source codes read
> 
> static PetscErrorCode PCSetUp_Composite(PC pc)
> 168: {
> 169:   PetscErrorCode   ierr;
> 170:   PC_Composite     *jac = (PC_Composite*)pc->data;
> 171:   PC_CompositeLink next = jac->head;
> 
> 174:   if (!jac->work1) {
> 175:    MatGetVecs(pc->pmat,&jac->work1,0);
> 176:   }
> 177:   while (next) {
> 178:     PCSetOperators(next->pc,pc->mat,pc->pmat,pc->flag);
> 179:     next = next->next;
> 180:   }
> 181:   return(0);
> 182: }
> Note the 178 line which calls PCSetOperators on pc0 and pc1.  The source codes of PCSetOperators
> read
> 
> 1050:  if (pc->setupcalled == 2 && flag != SAME_PRECONDITIONER) {
> 1051:     pc->setupcalled = 1;
> 1052:   }
> Note the 1051 line reset pc->setupcalled to 1, here the pc from PCSetUp_Composite is pc0 and pc1.
> So although if pc0  has been set up, this will cause pc0 be set up again. 
> 
> Is my reading correct?
> 
> When you change the operators, the preconditioner has to be set up again (perhaps not a "complete" setup, but some setup is required).

But I'm not *changing* the operator. It is PCSetUp_Composite that call PCSetOperators on sub pc
a second time-- he does not know that the sub pc has been set up before.


>  
> 
> Thanks a lot!
> Hui
> 
> 
>>  
>> 
>> 
>>> 
>>>  
>>> 
>>> Thanks!
>>> Hui
>>> 
>>> 
>>> > I have got a new question.  I'm now constructing a PCComposite from PCASM and another PCKSP (coarse
>>> > problem). And construction of PCKSP needs to use the subksp's of PCASM. So I need to PCSetUp on the
>>> > PCASM, right?  But the KSP using PCComposite would setup PCASM again.  How can I avoid twice setup
>>> > of PCASM ?
>>> 
>>> 
>> 
>> 
> 
> 

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