More precise yet widely applicable cost analysis

• Cost analysis aims at determining the amount of resources required to run a program in terms of its input data sizes. Automatically inferring precise bounds, while at the same time being able to handle a wide class of programs, is a main challenge in cost analysis. (1) Existing methods which rely on computer algebra systems (CAS) to solve the obtained cost recurrence equations (CR) are very precise when applicable, but handle a very restricted class of CR. (2) Specific solvers developed for CR tend to sacrifice accuracy for wider applicability. In this paper, we present a novel approach to inferring precise upper and lower bounds on CR which, when compared to (1), is strictly more widely applicable while precision is kept and when compared to (2), is in practice more precise (obtaining even tighter complexity orders), keeps wide applicability and, besides, can be applied to obtain useful lower bounds as well. The main novelty is that we are able to accurately bound the worst-case/best-case cost of each iteration of the program loops and, then, by summing the resulting sequences, we achieve very precise upper/lower bounds. 

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