computing the quartet distance between general trees
computing the quartet distance between general trees
computing the quartet distance between general trees
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22 CHAPTER 4. QUARTIC TIME ALGORITHMThis evidence makes it clear that it is in fact a worst-case quartic algorithm. In addition,<strong>the</strong> figure also reveals <strong>the</strong> interrelationship <strong>between</strong> <strong>the</strong> five groups of data. Observe that<strong>the</strong>re is a ra<strong>the</strong>r large difference in running time, with <strong>the</strong> star tree being <strong>the</strong> faster and<strong>the</strong> binary tree being <strong>the</strong> slower one to deal with. This seems natural, since <strong>the</strong> internalstructures of <strong>the</strong> <strong>trees</strong> are very different. The traversal of a tree with a complex internalstructure, a large number of internal nodes, is more time consuming and since <strong>the</strong> algorithmis based on a large number of traversals, this penalty is observable in <strong>the</strong> plots.And of course, <strong>the</strong> time bound is related to <strong>the</strong> number of leaves and not <strong>the</strong> internalstructure of <strong>the</strong> <strong>trees</strong>.This algorithm has shown – not surprisingly – to be very slow and not competitivewith a sub-cubic algorithm. It has merely worked as a reference of correctness, whenimplementing <strong>the</strong> o<strong>the</strong>r algorithms. Never<strong>the</strong>less, in Chapter 8, where all <strong>the</strong> results ofthis <strong>the</strong>sis are compared and discussed, <strong>the</strong> practical performance is compared to thoseof <strong>the</strong> o<strong>the</strong>r algorithms.