OP2/PyOP2 — pull request #352 by wence- (2014-04-07 17:17:56+00:00)
Title: Make matrix assembly a user-facing operation

The user may call multiple par_loops to insert into the same matrix, and
will only want to actually assemble it after the last one has
completed. Add a Mat.assemble() call which queues up (as a lazy
execution) the matrix assembly callback to allow this.