In our last primer we saw the Fourier series, which flushed out the notion that a periodic function can be represented as an infinite series of sines and cosines. While this is fine and dandy, and quite a powerful tool, it does not suffice for the real world. In the real world, very little is truly periodic, especially since human measurements can only record a finite period of time.

Problem: Derive the double angle identities $$\sin(2\theta) = 2\sin(\theta)\cos(\theta)\\\ \cos(2\theta) = \cos^2(\theta) – \sin^2(\theta)$$ Solution: Recall from linear algebra how one rotates a point in the plane. The matrix of rotation (derived by seeing where $ (1,0)$ and $ (0,1)$ go under a rotation by $ \theta$, and writing those coordinates in the columns) is $$A = \begin{pmatrix} \cos(\theta) & -\sin(\theta) \\\ \sin(\theta) &

Problem: Prove that $ 2 = 4$. Solution: Consider the value of the following infinitely iterated exponent: $$\displaystyle \sqrt{2}^{\sqrt{2}^{\sqrt{2}^{\cdot^{\cdot^{\cdot}}}}}$$ Let $ a_n = \sqrt{2} \uparrow \uparrow n$, that is, the above power tower where we stop at the $ n$-th term.

Overview In this primer we’ll get a first taste of the mathematics that goes into the analysis of sound and images. In the next few primers, we’ll be building the foundation for a number of projects in this domain: extracting features of music for classification, constructing so-called hybrid images, and other image manipulations for machine vision problems (for instance, for use in neural networks or support vector machines;

The Complexity of Things Previously on this blog (quite a while ago), we’ve investigated some simple ideas of using randomness in artistic design (psychedelic art, and earlier randomized css designs). Here we intend to give a more thorough and rigorous introduction to the study of the complexity of strings.

Main Theorem: There exist optimal stackings for standard two-player Texas Hold ‘Em. A Puzzle is Solved (and then some!) It’s been quite a while since we first formulated the idea of an optimal stacking. In the mean time, we’ve gotten distracted with graduate school, preliminary exams, and the host of other interesting projects that have been going on here at Math ∩ Programming.

Problem: Prove that generalized versions of Mario Brothers, Metroid, Donkey Kong, Pokemon, and Legend of Zelda are NP-hard.

Problem: Remember results of a function call which requires a lot of computation. Solution: (in Python) def memoize(f): cache = {} def memoizedFunction(*args): if args not in cache: cache[args] = f(*args) return cache[args] memoizedFunction.cache = cache return memoizedFunction @memoize def f(): ... Discussion: You might not use monoids or eigenvectors on a daily basis, but you use caching far more often than you may know.

Problem: Write a program that shuffles a list. Do so without using more than a constant amount of extra space and linear time in the size of the list.

By the end, the breadth and depth of our collective knowledge was far beyond what anyone could expect from any high school course in any subject. Education Versus Exploration I’m a lab TA for an introductory Python programming course this semester, and it’s been…depressing.

Not Just Time, But Space Too! So far on this blog we’ve introduced models for computation, focused on Turing machines and given a short overview of the two most fundamental classes of problems: P and NP. While the most significant open question in the theory of computation is still whether P = NP, it turns out that there are hundreds (almost 500, in fact!) other “classes” of problems whose relationships are more or less unknown.