520 ANSWERS TO EXERCISES 3.1 The desired average
520 ANSWERS TO EXERCISES 3.1 The desired average value can now be computed; it is (cf. exercise 12) E,,, = ;(HI + 2H$$ + 3H3 - +f~~+…. =1+j m This latter formula was obtained by quite different means by Martin D. Kruskal, AMM 61 (1954), 392-397. Using the integral representation he proved the asymptotic relation lim,,, (Em -$ lnm) = i(r + ln2). For further results and references, see John Riordan, Annals Math. Stat. 33 (1962), 178-185. 15. The probability that f(s) # z for all x is (m-l) /m, which is approximately l/e. The existence of a self-repeating value in an algorithm like Algorithm K is therefore not colossal at all-it occurs with probability 1 - l/e M .63212. The only colossal thing was that the author happened to hit such a value when X0 was chosen at random (see exercise 11). 16. The sequence will repeat when a pair of successive elements occurs for the second time. The maximum period is m2. (Cf. next exercise.) 17. After selecting Xc,. . . , Xk-1 arbitrarily, let Xn+l = f(Xn, , Xn-kfr), where 0
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