Problem 7. (20 pts) Let n N be a natural number and X a finite set...
Problem 7. (20 pts) Let n EN be a natural nmber and X a finite set with n elements. Show that the number of permutations of X such that no element stays in the same position is n! k! k o For instance, there are 6 = 3! permutations of 3 elements, but only 2 of them are permutations which fix no element. Similarly, there are 24-4! permutations of 4 elements, but only 9 which fix no element. Hint: Use...
Problem 5. (20 pts) Let n E N be a natural number and let X C N be a subset with n +1 elements. Show that there exist two natural numbers x,y X such that x-y is divisible by n
Let X be a finite set and F a family of subsets of X such that every element of X appears in at least one subset in F. We say that a subset C of F is a set cover for X if X =U SEC S (that is, the union of the sets in C is X). The cardinality of a set cover C is the number of elements in C. (Note that an element of C is a...
7. Let A, , An be non-empty subsets of a finite set Ω. If 1 k n and Ek is the set of elements in Ω which belong to at least k of the Ai's show that Pal i-1
7. Let A, , An be non-empty subsets of a finite set Ω. If 1 k n and Ek is the set of elements in Ω which belong to at least k of the Ai's show that Pal i-1
Problem 7. Fix a natural number n € N, and let en denote the equivalence relation "modulo n" on Z defined by x =n y if and only if n|y-r. axun (a) (6 points) Prove that pe N is prime, and if a, b € Z with a? Ep 62, then either a = b or a =p -b. (b) (4 points) Provide a counterexample showing the result in (a) may fail when p is not prime. That is, find...
Problem 5. (20 pts) Let r,n N be two natural numbers with r < n. An r x n matrix M consisting of r rows and n columns is said to be a Latin rectangle of size (r, n), if all the entries My belong to the set {1,2,3,..., n), for 1Si<T, 1Sj<T, and the same number does not appear twice in any row or in any column. By defini- tion, a Latin square is a Latin rectangle of size...
Let f [n]n] be a permutation. A fixed point of f is an element x e [n] such that f(x)-x. Now consider random permutations of [n] and let X be the random variable which represents the number of fixed points of a given permutation. (a) What is the probability that X 0? (b) What is the probability that X 2? (c) What is the probability that X--1? (d) What is the expectation of X? (Hint: As usual, express X as...
7.15· Let X be a finite set on which a neighborhood structure is defined: that is, each x E 2 has a set of neighbors N(x). Let n be the number of neighbors of x e 2. Consider a Metropolis-Hastings algorithm with proposal density q(y | x) l/nx for all y E N(x). That is, from a current state x, the proposal state is drawn from the set of neighbors with equal probability. Let the acceptance probability be Assuming the...
(1) Let f : [n] [n] be a permutation. A fixed point of f is an element x e [n] such that f(x) - x. Now consider random permutations of [n] and let X be the random variable which represents the number of fixed points of a given permutation. (a) What is the probability that X 0? (b) What is the probability that X-n -2? (c) What is the probability that X-n-1? (d) What is the expectation of X? (Hint:...
Let X be a finite set on which G acts, let ρ be the corresponding permutation representation [cf. 1.2, example (c)], and xx be the character of p. Let s E G; show that xx(s) is the number of elements of X fixed by s.
Let X be a finite set on which G acts, let ρ be the corresponding permutation representation [cf. 1.2, example (c)], and xx be the character of p. Let s E G; show that xx(s)...