On Tue, Mar 4, 2014 at 11:59 AM, Fande Kong <[email protected]> wrote:
> Jed, > > Thanks, > > I readed the node you gave. I still have some questions. > > (1) One root can be related with zero, one or many leaves, right? One leaf > only can be related with zero or one root. > Yes, that is what makes it a tree, rather than a DAG. > (2) In Algorithms section. Could you please give me a very simple example > to demonstrate how 'Extracting a submatrix from a sparse matrix', ' > Ownership discovery and transfer' and 'Graph distribution'. The description > is hard for me to understand. > These are not simple things. What exactly are you looking for? You can see graph distribution done with PetscSF in DMPlexDistribute(). Matt > Fande, > > > On Mon, Mar 3, 2014 at 5:54 PM, Jed Brown <[email protected]> wrote: > >> Fande Kong <[email protected]> writes: >> >> > Hi all, >> > >> > I was wondering mechanisms of the object PetscSF. What are definitions >> of >> > roots and leaves? Do roots/leaves associate with the data we want to >> > receive/send? For the function Bcast, it seems that we transfer data >> from >> > roots to leaves. But in another function Reduce, it seems that we move >> data >> > in the opposite direction (from leaves to roots). These kind of >> mechanisms >> > possibly make users confused. >> >> The SF graph is asymmetric so that it can have cleaner semantics. Read >> my note and reply here if something is still unclear. >> >> http://59a2.org/files/StarForest.pdf >> > > -- What most experimenters take for granted before they begin their experiments is infinitely more interesting than any results to which their experiments lead. -- Norbert Wiener
