You mean I need to let all processes have a copy of the whole global index and to use this function? thanks
On Fri, Jan 2, 2009 at 5:15 PM, Barry Smith <bsmith at mcs.anl.gov> wrote: > > The ix and iy are always global indices based on where the vector lives. > > If you are going from a parallel to parallel vector then both indices are > "global" > > Barry > > > On Jan 2, 2009, at 2:21 PM, Yujie wrote: > > Dear Barry: >> >> I have a new question about the parameter "iy"(new index set of >> subvector). To parallel vector, how to provide "ix" and "iy"? >> >> Just providing the local index subset for "ix" and "iy"? if it is, it is a >> little difficult to let the local vector know its global position in the new >> subvector? If the user needs to provide the global position of local vector >> for "iy". some MPI communication should be needed, it looks like not a good >> method. In exacting submatrix, the function hides this problem. could you >> give me any comments? thanks a lot. >> >> Regards, >> >> Yujie >> >> >> On Fri, Jan 2, 2009 at 11:46 AM, Barry Smith <bsmith at mcs.anl.gov> wrote: >> >> VecScatter is for this purpose. >> >> Rational: extracting subparts of vectors for ghost points etc takes place >> many times in a simulation; maybe millions. >> Thus separating it into a set-up followed by many uses is a worthwhile >> optimization. Extracting submatrices occur >> much less often in a simulation, maybe tens, hundreds or thousands of >> times so it is not worth the extra complexity >> of having separate set-up followed by many uses. One could argue that >> uniformity of design means we should have >> handled matrices with a MatScatter concept to parallel the Vec approach, >> but it is too late now :-). >> >> Barry >> >> >> On Jan 2, 2009, at 1:41 PM, Yujie wrote: >> >> Like MatGetSubMatrix(), whether is there a function to get a subvector in >> parallel mode? I have checked some scatter functios, they don't likely work. >> thanks a lot. >> >> Regards, >> >> Yujie >> >> >> >> > -------------- next part -------------- An HTML attachment was scrubbed... URL: <http://lists.mcs.anl.gov/pipermail/petsc-users/attachments/20090102/6cc0ee6a/attachment.htm>
