6
Three Components
•Reduction op<<A has three parts:
–Initialization … first step is initial_val op A[1]
–Local Combine … intermed_val op A[i]
–Global Combine … intermed_val op intermed_val
•Users define all three (overloaded with the same name) using standard procedure syntax
• Æ Ä 3 Ä 1 Ä 4 Ä 1    Æ Ä 5 Ä 9 Ä 2 Ä 6
Initialization
Local
P1 result
ÄP2 result
Global