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Lecture 4 Sorting Networks
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Comparator comparator
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A Sorting Network 9 5 2 6 5 9 2 6 2 5 6 9 2 5 6 9 A sorting network is a comparison network which output monotone nondecreasing sequence for every input.
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Depth 9 5 2 6 5 9 2 6 2 5 6 9 2 5 6 9 Depth is the maximum number of comparators on a path from an input wire to an output wire.
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Depth = parallel time 9 5 2 6 5 9 2 6 2 5 6 9 2 5 6 9 Depth is the maximum number of comparators on a path from an input wire to an output wire.
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Insertion Sort
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key
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Sorting network constructed from insertion sort.
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How to construct a sorting network from merging sort?
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Divide and Conquer Divide the problem into subproblems. Conquer the subproblems by solving them recursively. Combine the solutions to subproblems into the solution for original problem.
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Merge Sort
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Procedure
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Structure Sorting network Sorting network Merging network
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Construction of Merging Network 0-1 principal. Bitonic sorter. Merging network.
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0-1 principal
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Lemma
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Proof of 0-1 Principal
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Bitonic Sequence
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Bitonic 0-1 Sequence
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Some Properties
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The half-cleaner bitonic clean bitonic 0 0 0 0 1 0 1 1 0 0 1 1 1 0 0 0
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The half-cleaner bitonic clean bitonic 0 0 1 0 1 1 1 1 0 0 1 1 1 1 1 0
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Lemma (a)One of two halfs is bitonic clean. (b) every number in the 1 st half ≤ any element in the 2 nd half.
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Proof (case 1) 1 0 0 1 0 0 1 0 0
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Proof (case 2) 1 0 0 1 0 0 1 0 0
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Proof (case 3) 1 0 0 1 0 0 1 0 0 1 1
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Proof (case 4) 1 0 0 1 0 0 1 0 0 1 1
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Proof (case 5) 1 0 0 1 0 1 1 1 1 1 1
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Proof (case 6) 1 0 0 1 0 1 1 1 1 1 1
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Proof (case 7) 1 0 0 1 0 1 1 1 1 0 0
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Proof (case 8) 1 0 0 1 0 1 1 1 1 0 0
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Half cleaners bitonicsorted
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Half cleaners sorted 0 0 1 1 0 0 0 1 0 0 0 0 0 1 1 1 Merging Network
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Structure Sorting network Sorting network Merging network
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Merging Networks Sorting Network
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What we learnt in this lecture? What is sorting network? Depth = parallel time. Sorting network from Merge sort.
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Permutation Network Switching network Rearrangeability Nework with 2x2 crossbars
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Crossbar Switch A crossbar switch can realize any matching between Inputs and outputs.
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3-stage Clos Network 1 m n n n n
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Rearrangeability Theorem
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Network with 2x2 crossbars
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Puzzle
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