**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?

Wed Mar 31 10:08:15 EST 1999