The UMD overlapper is designed to reduce the number of overlaps produced by the assembler by reducing the number of repeat-induced overlaps. Furthermore the algorithm is greatly enhanced through the use of minimizers - a technique for reducing the number of k-mers considered in the initial phase of overlapping by an order of magnitude. Most assemblers use exact k-mer matches in order to identify reads that potentially overlap.
In conjunction with the UMD overlapper, the UMD error corrector identifies and corrects potential sequencing errors by detecting bases in a multiple alignment of reads that are supported by only one of the reads. The algorithm uses a heuristic rule called the 4-3 rule that examines overlapping sets of 4 reads at 3 positions in order to identify differences corresponding to distinct copies of a repeat.
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