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Definition of polyphase merge sort, possibly with links to more information and implementations. POLYPHASE MERGE SORTING — AN ADVANCED TECHNIQUE. R. L. Gilstad. Minneapolis-Honeywell Regulator Company. Electronic Data Processing. This article demonstrates one of the best known merge sorts, the polyphase merge. I make no sensational claims regarding the performance of this particular .
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To work with either lists or arrays you need a container implementation. You can also execute Sort on any number of input files, one at a time, as long as the size of the input polyphase merge sort elements remains constant. The technique provisionally allows you to write a comparison function that takes arguments of ppolyphase specific type you’re interested in, without resorting to casting. An ordinary merge sort using four working files organizes them as a pair of input files and a pair polyphase merge sort output files.
We would then merge 8 runs untillT2 was empty which would leave 5 runs sott on T1 and 8 runs on T3. For polyphase merge sort, an input file with 13 runs would write 5 runs to file 1 and 8 runs to polyphase merge sort 2. Initially m records are read into memory and placed in a priority queue. We can do so by using priority queue.
The initial distribution is set up so that only polyphase merge sort input working file is emptied at a time, except for the final merge iteration which merges N-1 single runs of varying size, this is explained next from polyphqse N-1 input working files to the single output file, resulting in a single sorted run, the sorted dataset.
Note that xort a file of the same name exists before calling the sort, RenameOutput will not succeed Listing 3. Views Read Edit View history. Without an active list, the merge would need to inspect an end-of-run flag each time around the merge list while scanning for the next polyphase merge sort element to remove.
The merge will frequently account for all null runs on the first pass, unless a dummy merge produced a null run on the target. Polyyphase is hereby granted to use this code including derivations in any manner provided this copyright notice appear appropriately in source. Each merge iteration merges runs from the two input working files, alternating the merged output between the two output files, again distributing the merged polyphase merge sort evenly between the two output files until the final merge iteration.
Assume run size is 1 element, 31 runs, 4 tapes. The Art of Computer Programming, Volume 3: All logging functions appear on the ftp site in files sortlog. Srt polyphase sort needs to transfer only a portion of the data at each polyphase merge sort, resulting in higher overall efficiency since much less data movement occurs. A second polyphase merge sort phase then makes one or more passes across the work files, merging runs to form longer runs on polypnase pass.
To realize this degree of efficiency, the initial distribution of runs in polhphase work files must conform to a sequence of Fibonacci numbers.
Merging one or more dummy runs mmerge one or more real runs just merges the real runs, and merging one or more dummy runs with no real runs results in a single dummy run. We start with k runs, then we copy those runs to 2 input tapes on the left on polyphase merge sort pic beloweach iteration we take two different runs from the input tapes, merge and sort them, and polyphase merge sort one iteration save merfe to the first output tape, mergs in next iteration – to the second one, as shown below.
To give you some idea of performance, I offer a few test results Figures 3 and 4. Truncated to zero length, it becomes the new target file for the next merge pass. Polyphase merge sort Wikipedia, the free encyclopedia. Block merge sort Timsort Introsort Spreadsort.
The main sorting routine is none the wiser. To raise sorting efficiency to acceptable levels for large source files, depending on the operating environment it must manage memory allocation more effectively to use larger merge buffers.
Wiki has an article on polyphase merge sort. Polyphase merge sort initial distribution, run count: After the initial distribution, an ordinary merge sort using 4 polyphase merge sort will sort 16 single record runs in 4 iterations of the entire dataset, moving a total of 64 records in order to sort the dataset after the initial distribution.
The polyphase merge gains maximum efficiency relative to other merge sorts from its particular method of distributing data runs. Finally, my question is: Polyphase merge sort is the fastest way to do a sort using 3 megre.
What is the number of phases Polyphase merge sort from the original on