On Sep 27, 2010, at 11:30 AM, Jed Brown wrote: > On Mon, Sep 27, 2010 at 18:24, Barry Smith <bsmith at mcs.anl.gov> wrote: >> >> We need an efficient MatAXPY() that works well for any combination of >> nonzero patterns. This is not terribly difficult to write. Basically for >> each row create a linked list of the nonzeros in it from the first matrix >> and then merge in the nonzeros from the second matrix for that row, much >> like in the LU symbolic factorizations. This will give you row counts, then >> preallocate the correct nonzero matrix and do the MatSetValues() for the >> first matrix first row then the second matrix first row etc. Finally swap in >> the new matrix body into the current matrix. > > I don't see why you'd need a linked list for this, you have two sorted > arrays (one for each row) and just need to count the number of unique > elements. It's one loop.
You need to merge the two arrays, don't you? I was suggested the linked list to do the merge, but I am sure you are correct there are other better ways to do merges. Barry > > Jed
