Parallel Processing
Merge sort parallelizes well due to use of the divide-and-conquer method. A parallel implementation is shown in pseudo-code in the third edition of Cormen, Leiserson, and Stein's Introduction to Algorithms. This algorithm uses a parallel merge algorithm to not only parallelize the recursive division of the array, but also the merge operation. It performs well in practice when combined with a fast stable sequential sort, such as insertion sort, and a fast sequential merge as a base case for merging small arrays. Merge sort was one of the first sorting algorithms where optimal speed up was achieved, with Richard Cole using a clever subsampling algorithm to ensure O(1) merge. Other sophisticated parallel sorting algorithms can achieve the same or better time bounds with a lower constant. For example, in 1991 David Powers described a parallelized quicksort (and a related radix sort) that can operate in O(log n) time on a CRCW PRAM with n processors by performing partitioning implicitly.
Read more about this topic: Merge Sort
Famous quotes containing the word parallel:
“We tend to be so bombarded with information, and we move so quickly, that there’s a tendency to treat everything on the surface level and process things quickly. This is antithetical to the kind of openness and perception you have to have to be receptive to poetry. ... poetry seems to exist in a parallel universe outside daily life in America.”
—Rita Dove (b. 1952)