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In a Cellular Automaton a puffer train, or simply '''puffer''', is a finite pattern that moves itself across the "universe", leaving debris behind. Thus a pattern consisting of only a puffer will grow arbitrarily large over time. Puffers differ from Spaceship s in that spaceships do not leave debris behind. Nonetheless, puffers are considered to have '''periods''' and '''speeds''' in the same way that spaceships have. (See the article on Spaceship s for more information.) The period of a puffer can be considered as the combination of ''two'' periods; the first is the period of the puffer itself, while the second is the apparent period of the pattern of debris produced. This is often the same as the period of the puffer, but sometimes is a factor of the period. A puffer for which the apparent period deduced from the debris is smaller than the period of the engine is a pseudoperiod puffer. Such puffers are typically produced by artificial means. A '''true period puffer''' is one in which the period of the debris matches that of the puffer. Puffers are divided into two classes, dirty puffers and '''clean puffers'''. While there is no precise distinction, a '''dirty''' puffer is one in which there is little apparent order in the debris (although the debris will still eventually be periodic). A '''clean''' puffer, conversely, has a small amount of debris that appears much more organized. A dirty puffer can sometimes be turned into a clean puffer by adding spaceships of the same velocity as the puffer that affect what debris results. A puffer whose debris consists entirely of spaceships is called a Rake . IN CONWAY'S GAME OF LIFE The first known puffer, in for three reasons: First, if they can be stabilized in such a way that they produce only gliders (that is, turned into rakes) they can be used as part of many more complex patterns such as breeders. Second, stabilizations of puffers that eliminate all of their output debris can be used to produce spaceships with arbitrarily large periods. And third, puffers can sometimes be tamed or combined to form spaceships with speeds that do not seem to be achievable in other ways; for instance, in Life, the ''switch engine'' is a puffer train discovered by Charles Corderman that moves diagonally at speed ''c''/12, and in 1991 Dean Hickerson showed how to combine several switch engines to form a ''c''/12 spaceship that he called the ''Cordership''. Corderships and puffers, D. Hickerson . Cordership, E. Weisstein . Cordership, Lifepage . REFERENCES |
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