random walk
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 S.R. Srinivasa Varadhan
random walk, in probability theory, a process for determining the probable location of a point subject to random motions, given the probabilities (the same at each step) of moving some distance in some direction. Random walks are an example of Markov processes, in which future behaviour is independent of past history. A typical example is the drunkard’s walk, in which a point beginning at the origin of the Euclidean plane moves a distance of one unit for each unit of time, the direction of motion, however, being random at each step. The problem is to find, after some fixed time, the probability distribution function of the distance of the point from the origin. Many economists believe that stock market fluctuations, at least over the short run, are random walks.
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