Basic HTML version of Foils prepared 19 September 98

Foil 16 Why use Process Groups?

From MPI Message Passing Interface Computational Science for Simulations -- Fall Semester 1998. by Geoffrey C. Fox, Nancy McCracken
We find a good example when we consider typical Matrix Algorithm
  • (matrix multiplication)
  • A i,j = ?k B i,k C k,j
  • summed over k'th column of B and k'th row of C
Consider a block decomposition of 16 by 16 matrices B and C as for Laplace's equation. (Efficient Decomposition as we will see later)
Each sum operation involves a subset(group) of 4 processors
k = 2

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