Browsing by Author "Phan, Thong H."

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    ACCELERATING SEARCH IN FUNCTION INDUCTION
    (1989-11-01) Phan, Thong H.; Witten, Ian H
    Inducing functions from examples is an important requirement in many learning systems. Blind search is the most general approach, but is vastly less efficient than specialized problem-solving methods. This paper presents a new strategy to accelerate search without sacrificing generality. Experiments with numeric functions show several orders of magnitude performance increase over the standard search technique. Two factors account for this improvement. First, the new strategy manipulates functions in groups instead of singly, so that many can be selected or discarded with only one comparison. Second, functional equivalence is handled automatically by the internal organization of search space.
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    LINUS: AN INTERACTIVE SYSTEM FOR FUNCTION DISCOVERY
    (1993-09-01) Witten, Ian H.; Phan, Thong H.
    Function discovery is the problem of finding a symbolic formula for an unknown function from examples of the function's value on certain arguments. This paper describes the design, implementation and operation of a function discovery system that differs from previous ones in two principal ways. First, it is interactive: it proceeds from a partial set of examples and requests additional ones where needed. Second, it expresses the solution implicitly, as a small system of simultaneous equations, some of which may be differential equations. Solving these symbolically would (if it were possible) give a formula for the unknown function. The system can discover a wide range of functions, including all rational functions and those that can be transformed to rational functions by differentiation and logarithm operations.