Tag Archives: generating functions

Burnside’s Lemma and Polya Enumeration Theorem (2)

[ Acknowledgement: all the tedious algebraic expansions in this article were performed by wolframalpha. ] Counting Graphs One of the most surprising applications of Burnside’s lemma and Polya enumeration theorem is in counting the number of graphs up to isomorphism. … Continue reading

Posted in Notes | Tagged , , , , , , , , | Leave a comment

Random Walk and Differential Equations (I)

Consider discrete points on the real line, indexed by the integers … -3, -2, -1, 0, 1, 2, … . A drunken man starts at position 0 and time 0. At each time step, he may move to the left … Continue reading

Posted in Notes | Tagged , , , | Leave a comment

Power Series and Generating Functions (IV) – Exponential Generating Functions

Note: this article is noticeably more difficult than the previous instalments. The reader is advised to be completely comfortable with generating functions before proceeding. We’ve already seen how generating functions can be used to solve some combinatorial problems. The nice … Continue reading

Posted in Notes | Tagged , , , , , | 3 Comments

Power Series and Generating Functions (III) – Partitions

One particularly fruitful application of generating functions is in partition numbers. Let n be a positive integer. A partition of n is an expression of n as a sum of positive integers, where two expressions are identical if they can be obtained from each … Continue reading

Posted in Notes | Tagged , , , , , , | Leave a comment

Power Series and Generating Functions (I): Basics

[ Background required: basic combinatorics, including combinations and permutations. Thus, you should know the formulae and and what they mean. Also, some examples / problems may require calculus. ] Note: this post is still highly relevant to competition-mathematics. 🙂 To … Continue reading

Posted in Notes | Tagged , , , , , | Leave a comment