What are you trying to do by removing the rows/columns of the matrix? Are there any variables that you want to treat as constants and hence eliminating the rows and columns?
Shri On May 14, 2012, at 10:51 PM, Andrew Spott wrote: > Is there a computational cost to using a sparse matrix that is much bigger > than it should be? > > for example, say you have a matrix that is n x n, but you only store anything > in the first m rows and columns (m < n). > > Also, would you then have to redo the matrix distribution among nodes by > hand, or will PETSC do it for you? > > Thanks for the quick reply > > -Andrew > > On May 14, 2012, at 9:38 PM, Jed Brown wrote: > >> On Mon, May 14, 2012 at 9:33 PM, Andrew Spott <andrew.spott at gmail.com> >> wrote: >> What is the best way to selectively add/remove columns/rows of a Mat? >> >> Is there a way to do it in place, or does it require essentially moving the >> values to a new matrix? >> >> If you only need to add/remove a small number of values, it's best to >> allocate for all that might be present and just store explicit zeros. >> >> To add or remove rows, you are also changing the vector size that can be >> multiplied against, and the data structure must be rebuilt. This is why it's >> frequently preferable to use MatZeroRows (or a variant) instead of removing >> them from the data structure. > -------------- next part -------------- An HTML attachment was scrubbed... URL: <http://lists.mcs.anl.gov/pipermail/petsc-users/attachments/20120514/ab63e191/attachment.htm>
