{"responseHeader":{"status":0,"QTime":6,"params":{"q":"{!q.op=AND}id:\"92699\"","hl":"true","hl.simple.post":"","hl.fragsize":"5000","fq":"!embargo_tdt:[NOW TO *]","hl.fl":"ocr_t","hl.method":"unified","wt":"json","hl.simple.pre":""}},"response":{"numFound":1,"start":0,"docs":[{"modified_tdt":"2015-11-02T00:00:00Z","thumb_s":"/58/2b/582b11613fc1b9ec759c93078eeaec4c4e84e952.jpg","oldid_t":"compsci 517","setname_s":"ir_computersa","file_s":"/7a/aa/7aaafad5a585a093878ef849335ab9f1d1e4bd87.pdf","title_t":"Page 18","ocr_t":"7 Speedup : Speedup S(p, n, A) is defined as ( ) Ts(n, S) S p,n,A = T(p,n,A) (2.1) where Ts( n, S) is execution time required to solve a given problem of size n with the best sequential algorithm S. Since we may not know the best sequential algorithm, we often consider it an ideal algorithm or a sequential complexity(i.e. minimal time) of solving the problem if known. Rough Speedup : Rough speedup R(p, n, A) is defined as a special case of S(p, n, A) when Ts(n, S) ~ T(1, n, A). Since T(1, n, A) is usually larger than Ts(n, S), rough speedup R(p, n, A) is a measurement that is favorable to parallel computing. If R(p, n, A) is greater than p, we say a speedup anomaly occurs for algorithm A with p processors. This case may happen when the sequential implementation of Sis not very efficient. Efficiency : Efficiency E is defined as E(p, n, A) = S(p;,A) Values of efficiency E range from 0 to 1 while rough efficiency that is analogous to the rough speedup may be greater than one. 2.2 Performance Degradation In typical cases the maximum efficiency Em is less than one. The performance degradation is caused by communicative or algorithmic overhead. Message passing mechanisms among processors must share computational resources that cannot be simultaneously devoted to advancing toward a solution directly. Especially for a distributed parallel computing(nonshared memory), it is often necessary to broadcast the data in order to reach agreement on the shared data, which generates","restricted_i":0,"id":92699,"created_tdt":"2015-11-02T00:00:00Z","format_t":"application/pdf","parent_i":92762,"_version_":1642982584341233665}]},"highlighting":{"92699":{"ocr_t":[]}}}