Remember the old cowboy movies? As the stage-coach comes to a halt, the wheels appear to spin backwards, then forwards, then backwards again, until the coach stops. How can this be explained?

## Posts Tagged 'Numerical Analysis'

### Can You Believe Your Eyes?

Published April 29, 2021 Occasional Leave a CommentTags: Numerical Analysis

### Does Numerical Integration Reflect the Truth?

Published July 23, 2020 Occasional Leave a CommentTags: Numerical Analysis, Numerical Weather Prediction

Many problems in applied mathematics involve the solution of a differential equation. Simple differential equations can be solved analytically: we can find a formula expressing the solution for any value of the independent variable. But most equations are nonlinear and this approach does not work; we must solve the equation by approximate numerical means. The big question is:

“*Does the numerical solution resemble the true solution of the equation?*”

The answer is: “*Not necessarily*”.

There are often specific criteria that must be satisfied to ensure that the answer `crunched out’ by the computer is a reasonable approximation to reality. Although the principles of numerical stability are quite general, they are best illustrated by simple examples. We will look at some of these below.

Continue reading ‘Does Numerical Integration Reflect the Truth?’

### Dimension Reduction by PCA

Published June 11, 2020 Occasional Leave a CommentTags: Algebra, Numerical Analysis

We live in the age of “big data”. Voluminous data collections are mined for information using mathematical techniques. Problems in high dimensions are hard to solve — this is called “the curse of dimensionality”. Dimension reduction is essential in big data science. Many sophisticated techniques have been developed to reduce dimensions and reveal the information buried in mountains of data.

### The Monte-Carlo Method

Published May 28, 2020 Occasional Leave a CommentTags: Algorithms, Numerical Analysis

Learning calculus at school, we soon find out that while differentiation is relatively easy, at least for simple functions, integration is hard. So hard indeed that, in many cases, it is impossible to find a nice function that is the integral (or anti-derivative) of a given one. Thus, given we can usually find , whereas we may not be able to find .

### The Rambling Roots of Wilkinson’s Polynomial

Published January 30, 2020 Occasional Leave a CommentTags: Algebra, Numerical Analysis

Finding the roots of polynomials has occupied mathematicians for many centuries. For equations up to fourth order, there are algebraic expressions for the roots. For higher order equations, many excellent numerical methods are available, but the results are not always reliable.

Continue reading ‘The Rambling Roots of Wilkinson’s Polynomial’

### Bouncing Billiard Balls Produce Pi

Published May 9, 2019 Occasional Leave a CommentTags: Algorithms, Numerical Analysis, Pi

There are many ways of evaluating , the ratio of the circumference of a circle to its diameter. We review several historical methods and describe a recently-discovered and completely original and ingenious method.

### Staying Put or Going with the Flow

Published February 1, 2018 Irish Times Leave a CommentTags: Algorithms, Geophysics, Numerical Analysis

The atmospheric temperature at a fixed spot may change in two ways. First, heat sources or sinks may increase or decrease the thermal energy; for example, sunshine may warm the air or radiation at night may cool it. Second, warmer or cooler air may be transported to the spot by the air flow in a process called advection. Normally, the two mechanisms act together, sometimes negating and sometimes reinforcing each other. What is true for temperature is also true for other quantities: pressure, density, humidity and even the flow velocity itself. This last effect may be described by saying that “the wind blows the wind” [TM132 or search for “thatsmaths” at irishtimes.com].

### Marvellous Merchiston’s Logarithms

Published November 17, 2016 Irish Times Leave a CommentTags: Applied Maths, History, Numerical Analysis

Log tables, invaluable in science, industry and commerce for 350 years, have been consigned to the scrap heap. But logarithms remain at the core of science, as a wide range of physical phenomena follow logarithmic laws [TM103 or search for “thatsmaths” at irishtimes.com].

### Simulating the Future Climate

Published March 6, 2014 Irish Times Leave a CommentTags: Computer Science, Geophysics, Numerical Analysis

The Earth’s climate is changing, and the consequences may be very grave. This week, *That’s Maths* in *The Irish Times* ( TM040 ) is about computer models for simulating and predicting the future climate.

### French Curves and Bézier Splines

Published February 6, 2014 Occasional Leave a CommentTags: Algorithms, Computer Science, Numerical Analysis

A French curve is a template, normally plastic, used for manually drawing smooth curves. These simple drafting instruments provided innocent if puerile merriment to generations of engineering students, but they have now been rendered obsolete by computer aided design (CAD) packages, which enable us to construct complicated curves and surfaces using mathematical functions called Bézier splines.

### Singularly Valuable SVD

Published February 14, 2013 Occasional Leave a CommentTags: Algebra, Algorithms, Computer Science, Numerical Analysis

In many fields of mathematics there is a result of central importance, called the “Fundamental Theorem” of that field. Thus, the fundamental theorem of arithmetic is the unique prime factorization theorem, stating that any integer greater than 1 is either prime itself or is the product of prime numbers, unique apart from their order.

The fundamental theorem of algebra states that every non-constant polynomial has at least one (complex) root. And the fundamental theorem of calculus shows that integration and differentiation are inverse operations, uniting differential and integral calculus.

**The Fundamental Theorem of Linear Algebra**

Continue reading ‘Singularly Valuable SVD’

### The Lambert W-Function

Published January 24, 2013 Occasional Leave a CommentTags: Analysis, Numerical Analysis

**Follow on twitter: @thatsmaths**

In a recent post ( The Power Tower ) we described a function defined by iterated exponentiation:

It would seem that when this must blow up. Surprisingly, it has finite values for a range of *x*>1. Continue reading ‘The Lambert W-Function’

### Carving up the Globe

Published October 18, 2012 Irish Times Leave a CommentTags: Algorithms, Geometry, Numerical Analysis, Spherical Trigonometry

**This week, That’s Maths (TM007) describes various ways of dividing up the sphere. This is an important problem in geometry, biology, chemistry, astronomy, meteorology and climate modelling. Continue reading ‘Carving up the Globe’**