[petsc-users] Could DMComposite handle two vectors with different grid sizes.

[Barry Smith]

  DMComposite doesn't say that the different DAs have to have the same dimensions, they can have different sizes, number of grid points etc

   Barry

On Jul 27, 2010, at 10:11 PM, (Rebecca) Xuefei YUAN wrote:

> Dear Barry,
> 
> I went over the mp1.c as the multi physics example. However, what I concerned is not addressed in that example. My concern is that will it be fine if the grid size for the different das are different.
> 
> The different grid sizes of da_A and da_B are coming from the fact that they share the same physical domain, but the computational domain are slightly different due to that problem A has the Neumann boundary condition (giving that the computational domain is half spacing extended from the physical domain, each point is expressed at the center of the cell) and problem B has the Dirichlet boundary condition (giving that the computational domain is the same as the physical domain, each point is expressed at the node of the cell.) Thus, problem A ALWAYS needs 1 more grid in each direction than problem B at each level.
> 
> If the coarsest grid has the difference 1(mA - mB = 1) in each direction, according to the algorithm for multigrid, the next finer level has the difference of ((2*mA-1) - (2*mB-1) = 2(mA-mB) = 2) in each direction, the next level has the difference of ((2*(2*mA-1)-1) - (2*(2*mB-1)-1) = 4*(mA-mB) = 4) in each direction. Because there is only half spacing being extended from the physical domain as the computational domain for problem A, the abandonNumber of grid is 1-1=0 for nl=1, 2-1=1 for nl=2 and 4-1=3 for nl=3.
> 
> To keep those extra points in the residual function and Jacobian, I applied the Neumann boundary condition for those points (mirror with the interior points).
> 
> Will this procedure be fine for such a multi physics problem?
> 
> Thanks very much!
> 
> Rebecca
> 
> 
> 
> 
> Quoting Barry Smith <bsmith at mcs.anl.gov>:
> 
>> 
>> 
>>   What you are doing below looks ok. This builds the DM and DMMG.   See tutorials/multiphysics/mp1.c for an example that uses SNES to  solve a nonlinear equation on the grids.
>> 
>>   Barry
>> 
>> 
>> 
>> On Jul 27, 2010, at 7:36 PM, (Rebecca) Xuefei YUAN wrote:
>> 
>>> Dear all,
>>> 
>>> If I have two different vectors (with different dof, stencil width  and grid sizes), could I use DMComposite to handle this?
>>> 
>>> The following is the piece of code for assemble this DMComposite in DMMG.
>>> 
>>> 	tempparameters.mxfield				= 5;
>>> 	tempparameters.myfield				= 5;
>>> 
>>> 	tempparameters.mxgrid	= tempparameters.mxfield+1;
>>> 	tempparameters.mygrid	= tempparameters.myfield+1;
>>> 
>>> 	ierr	= DMMGCreate(comm, tempparameters.numberOfLevels, &appCtx,  &dmmg);CHKERRQ(ierr);
>>> 
>>> 	ierr	= DMCompositeCreate(comm,&packer);CHKERRQ(ierr);
>>> 
>>> 	ierr	= DACreate2d(comm,DA_NONPERIODIC,DA_STENCIL_BOX,  tempparameters.mxfield, tempparameters.myfield, PETSC_DECIDE,  PETSC_DECIDE, 4, 3, PETSC_NULL, PETSC_NULL, &da_fff);CHKERRQ(ierr);
>>> 	ierr	= DASetFieldName(da_fff, 0, "phi");CHKERRQ(ierr);
>>> 	ierr	= DASetFieldName(da_fff, 1, "vz");CHKERRQ(ierr);
>>> 	ierr	= DASetFieldName(da_fff, 2, "psi");CHKERRQ(ierr);
>>> 	ierr	= DASetFieldName(da_fff, 3, "bz");CHKERRQ(ierr);
>>> 	ierr	= DACreate2d(comm,DA_NONPERIODIC,DA_STENCIL_BOX,  tempparameters.mxgrid, tempparameters.mygrid, PETSC_DECIDE,  PETSC_DECIDE, 1, tempparameters.gridStencilWidth, PETSC_NULL,  PETSC_NULL, &da_ggg);CHKERRQ(ierr);
>>> 	ierr	= DASetFieldName(da_ggg, 0, "disp");CHKERRQ(ierr);
>>> 
>>> 	ierr	= DMCompositeAddDM(packer,(DM)da_fff);CHKERRQ(ierr);
>>> 	ierr	= DMCompositeAddDM(packer,(DM)da_ggg);CHKERRQ(ierr);
>>> 	ierr	= DMCompositeAddArray(packer,0,1);CHKERRQ(ierr);
>>> 
>>> 	ierr	= DMMGSetDM(dmmg, (DM)packer);CHKERRQ(ierr);
>>> 
>>> 	ierr	= DADestroy(da_fff);CHKERRQ(ierr);
>>> 	ierr	= DADestroy(da_ggg);CHKERRQ(ierr);
>>> 
>>> .........................................................
>>> 
>>> 	ierr	= DMCompositeDestroy(packer);CHKERRQ(ierr);
>>> 	ierr	= DMMGDestroy(dmmg);CHKERRQ(ierr);
>>> 
>>> 
>>> I understand that for numberOfLevels(nl)>1, the grid size  difference is no longer 1, but 3(nl=2), 5(nl=3), could I use  DMComposite to handle such a case successfully?
>>> 
>>> I was not able to get examples for such a case, is there any?
>>> 
>>> Thanks a lot!
>>> 
>>> 
>>> 
>>> --
>>> (Rebecca) Xuefei YUAN
>>> Department of Applied Physics and Applied Mathematics
>>> Columbia University
>>> Tel:917-399-8032
>>> www.columbia.edu/~xy2102
>>> 
>> 
>> 
>> 
> 
> 
> 
> -- 
> (Rebecca) Xuefei YUAN
> Department of Applied Physics and Applied Mathematics
> Columbia University
> Tel:917-399-8032
> www.columbia.edu/~xy2102
>