Global Operations

• Reduce (<<)and scan (||) are array functionals that perform global operations

• +<<A reduces A to its sum

+<ɚ 4 6 8 ? 20

• +|| are parallel prefixes of A

+||2 4 6 8 ? 2 6 12 20

The operators are associative allowing parallel prefix techniques to be used in their evaluation

Reduce and scan apply only over applicable region

[1..i] firsti := +<<A; -- sum first i elements

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