LOYOLA COLLEGE (AUTONOMOUS), CHENNAI – 600 034

AB 15

   B.Sc. DEGREE EXAMINATION – MATHEMATICS

FIFTH SEMESTER – November 2008

MT 5406 – COMBINATORICS

 

 

 

Date : 14-11-08                     Dept. No.                                        Max. : 100 Marks

Time : 9:00 – 12:00

 

SECTION A

ANSWER ALL THE QUESTIONS:                                                                                (10×2 = 20 )

 

1. Define Binomial number.
2. Define Bell number.
3. Find the Ordinary generating function and Ordinary enumerator for the combinations of five symbols a, b, c, d, e.
4. Give all the partitions for 6.
5. Draw the Ferrers graph for λ = (764332). Also find λ.
6. Define h_λ and find h₄.
7. Prove that = pⁿ.
8. Find per .
9. Define derangement and deduce the formula for it using Sieve’s formula.
10. Define weight of a function.

 

SECTION B

ANSWER ANY FIVE QUESTONS:                                                                                (5×8 = 40 )

 

11. Give the recurrence formula for. Tabulate the values of for n, m = 1,2, …, 6.

 

12. Show that there exists a bijection between the following two sets:

(a) The set of n-tuples on m letters without repetition.

(b) The set of injections of an n-set into an m-set.

Prove that the cardinality of each of these sets is m (m-1) (m-2) … (m-n+1).

 

13. Prove that the elements f of R[t] given by f =has an inverse in R[t] if and only if  has an inverse in R.

 

 

14. Let n be a positive integer. Show that the Ordinary Enumerator,

• for the partitions of n is F(t) = .
• for the partitions of n into precisely m parts is .
• for the partitions of n into parts all of which are odd is .

15. Describe the monomial symmetric function and the elementary symmetric function with

an example.

 

16. State and prove Generalized inclusion and exclusion principle.
17. Define a rook polynomial. Prove with usual notation that R(t,) = t R(t, ) + R(t,).

 

18. List 6 elements of the group of rotational symmetries of a regular hexagon and their

types.

 

SECTION C

ANSWER ANY TWO QUESTIONS:                                                                              (2×20 = 40)

 

19. (i) Prove that number of distributions on n distinct objects into m distinct boxes with the

objects in each box arranged in a definite order is .

(ii) Define the combinatorial distribution with an example.

(15+5)

20. Explain in detail about the power sum symmetric functions.
21. (i) How many permutations of 1, 2, 3, 4 are there with 1 not in the 2^nd position, 2 not in

the 3^rd position, 3 not in the 1^st or 4^th position and 4 not in  the 4^th position.

(ii) Prove with the usual notation that.

(10+10)

22. State and prove the Burnside’s lemma.

 

 

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