> ?Well if they happen to be equal then it will never apply the transpose thus > giving a bad algorithm and garbage.
hmm, in the case when I provide a matrix for both Interpolate/Restrict, I have (M==N==Nx==Ny), this would always call the MatMult routine. As long as I provide both these operators/matrices explicitly, there is still no problem. A possible issue is only when someone provides just the restriction or prolongation. But I understand that when this happens, the other operator is computed explicitly as its transpose. If this is actual implementation, I still dont see a problem. Although, if the restriction/prolongation operator are implicitly assumed to be transpose of the other, then it will quite horribly fail since only MatMult is called for both. I am not completely sure about the mode currently used in petsc but it would be great if you can help me understand. Note: I probe more on this since my linear tesselation (most often) results in the same number of dofs on the coarser level (p-coarsened/h-refined) and I dont want a glitch to come back and bite me later on.. Vijay On Wed, Dec 15, 2010 at 8:36 PM, Barry Smith <bsmith at mcs.anl.gov> wrote: > > On Dec 15, 2010, at 8:16 PM, Vijay S. Mahadevan wrote: > >> Barry, >> >> Thanks for the prompt change ! I do not work on the development >> version but I can update these matrix routines alone. >> >>> ?Note it can still glitch if the restricted size is exactly the original >>> size. :-( >> >> Why would it glitch if the restricted size is the same as the original >> size though ? I dont see a case where your check (M==Ny) would fail. >> Can you please elaborate more on this ? > > ?Well if they happen to be equal then it will never apply the transpose thus > giving a bad algorithm and garbage. > > ?Barry > >> >> Vijay >> >> On Wed, Dec 15, 2010 at 8:04 PM, Barry Smith <bsmith at mcs.anl.gov> wrote: >>> >>> ?I have pushed this change to petsc-dev and it is ready for use. >>> >>> ? Barry >>> >>> ?Note it can still glitch if the restricted size is exactly the original >>> size. :-( >>> >>> >>> On Dec 15, 2010, at 7:53 PM, Barry Smith wrote: >>> >>>> >>>> ?Vijay, >>>> >>>> ? ?The use of M>N in MatRestrict and MatInterpolate was always a bit >>>> cheesy since it has this broken case that you reported. I will change it >>>> to do as you suggest and use the size of the vectors in determining which >>>> way to apply. But note I will do this in petsc-dev >>>> http://www.mcs.anl.gov/petsc/petsc-as/developers/index.html not petsc-3.1 >>>> so you'll need to switch if you are not using petsc-dev. >>>> >>>> ? I'll try to get it down in the next few hours but it may take a little >>>> longer. >>>> >>>> >>>> ? Barry >>>> >>>> On Dec 15, 2010, at 6:06 PM, Vijay S. Mahadevan wrote: >>>> >>>>> Hi, >>>>> >>>>> I have an implementation issue with the MatRestrict/Interpolate >>>>> functions. The problem is that one of my coarser levels (with PCMG) >>>>> has higher dofs than the finest level. This does not always happen and >>>>> requires a weird fine mesh system (in a sense) that uses multi-grid, >>>>> but the idea is that the finest level problem has a high order (HO) >>>>> discretization while the lower level mesh has a linear tesselation of >>>>> the finest HO level (which I can optimize) and then adaptively >>>>> coarsened levels beyond that. Since the number of columns in this case >>>>> is larger than the number of rows, MatRestrict invariably calls >>>>> MatMultTranspose to multiply instead of MatMult and vice-versa while >>>>> calling ?MatInterpolate. These result in assertion errors while >>>>> comparing the length of Mat and Vec. The chosen method is based on >>>>> whether (M>N) which seems to act against what I am doing here... >>>>> >>>>> I can always implement a shell matrix to replicate >>>>> Restrict/Interpolate actions but my question is whether if such >>>>> discretization will yield a consistent convergence in MG algorithm ? >>>>> Is there a strong reason for checking if (M>N) rather than just doing >>>>> (mat->rmap->N==y->map->N && mat->cmap->N==x->map->N) ? I would >>>>> appreciate any detailed answer that you can provide for this and any >>>>> suggestions to use the existing methods (without implementing the >>>>> shell restriction) is very welcome. >>>>> >>>>> Thanks, >>>>> vijay >>>> >>> >>> > >
