Special Cases of Parallel Prefix Networks, II
Tom Kelliher, CS 315
Mar. 31, 1999
Reading from last time.
Began special cases.
- Parallel prefix on networks.
- Parallel segmented prefix computations.
Carry save, multiplication, convolution.
Recall idea: each vertex of the network simulates a leaf and an internal
vertex of the tree.
Consider this example:
- Compute the breadth-first spanning tree from A.
- Is the tree unique?
- Run parallel prefix on the resulting tree.
Definition:
A sequence of prefix computations that use the same associative operator
, but on disjoint sets of data.
Example: Addition on 
.
- Obviously, we can solve using three prefix computations. With a
trick, we can do it in one.
- The trick: use
| as a barrier symbol at the start of each set
of data.
- The data set:
|2, 3, |1, 7, 2, |1, 3, 6.
Redefine our operator:
``Forget about everything to the left of the barrier.''
- Run the example.
- What is the running time of the parallel segmented prefix
computation?
Thomas P. Kelliher
Wed Mar 31 10:08:15 EST 1999
Tom Kelliher