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Figure B–5 LU Decomposition with (*, BLOCK) Distribution MLO-011936 Computation is done on progressively smaller submatrices in the lower right-hand corner of the array. The first panel of the figure shows the first iteration of the DO loop in which the entire array is worked on by all four processors. The second panel shows the seventh iteration, by which time Peer 0 is completely idle because none of the elements of the submatrix are stored in its memory. The third panel of the figure shows the eleventh iteration of the DO loop, by which time both Peer 0 and Peer 1 are idle. The fourth panel shows the fifteenth iteration, where only Peer 3 is working, with the other three processors idle. For most of time spent in the DO loop, one or more processors are left idle. B–16 HPF Tutorial: LU Decomposition
