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Category Archives: Notes
Power Series and Generating Functions (II): Formal Power Series
For today’s post, we shall first talk about the Catalan numbers. The question we seek to answer is the following. Let n be a positive integer. Given a non-associative operation *, find the number of ways to bracket the expression … Continue reading
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Tagged catalan numbers, combinatorics, formal power series, intermediate, power series
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Symmetric Polynomials (III)
Now we generalise this to n variables: . It’s clear what the corresponding building blocks of symmetric polynomials would be: ; ; ; … . We call these ei‘s the elementary symmetric polynomials in the xi‘s. Note that each ei is the coefficient of Ti in the … Continue reading
Symmetric Polynomials (II)
When we move on to n=3 variables, we now have, as basic building blocks, These are just the coefficients of in the expansion of . Once again, any symmetric polynomial in x, y, z with integer coefficients can be expressed as a polynomial … Continue reading
Symmetric Polynomials (I)
[ Background required: knowledge of basic algebra and polynomial operations. ] After a spate of posts on non-IMO related topics, we’re back on track. Here, we shall look at polynomials in n variables, e.g. P(x, y, z) when n = 3. Such … Continue reading
Modular Arithmetic Deluxe Edition
[ Background required: standard modular arithmetic. ] Consider the following two problems: Problem 1. Prove that if p > 2 is prime, then when is expressed in lowest terms , m must be a multiple of p. Problem 2. Prove that if … Continue reading
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Tagged basic, congruence, modular arithmetic, notes, number theory, rational numbers
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Linear Algebra: Inner Products
[ Background required: basic knowledge of linear algebra, e.g. the previous post. Updated on 6 Dec 2011: added graphs in Application 2, courtesy of wolframalpha.] Those of you who already know inner products may roll your eyes at this point, … Continue reading
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Tagged advanced, extra, fourier transform, inner product, intermediate, linear algebra, notes, sums
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Estimating Sums Via Integration
Background required : calculus, specifically integration By representing a sum as an area, it is often possible to estimate its size by approximating it with the area underneath a curve. For example, suppose we wish to compute the sum . … Continue reading
Sample Problem Solving + Homework Hints
In this post, I’ll talk about basic number theory again. But I’ll still assume you already know modular arithmetic. 🙂 In the first part, there’ll be some sample solutions for number theoretic problems, some of which were already presented in … Continue reading
Quadratic Residues – Part IV (Applications)
Let p be an odd prime and g be a primitive root modulo p. Given any a which is not a multiple of p, we can write for some r. We mentioned at the end of the last section that a is a square if … Continue reading
Mathematics and Such 