An isometry on a metric space is a one-to-one distance-preserving transformation on the space. The Euclidean group is the group of isometries of -dimensional Euclidean space. These are all the transformations that preserve the distance between any two points. The group depends on the dimension of the space. For the Euclidean plane , we have the group , comprising all combinations of translations, rotations and reflections of the plane.

## Posts Tagged 'Algebra'

### 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.

### Bang! Bang! Bang! Explosively Large Numbers

Published March 26, 2020 Occasional Leave a CommentTags: Algebra, Number Theory

which is approximately . The number of atoms in the universe is estimated to be about . When we consider permutations of large sets, even more breadth-taking numbers emerge.

Continue reading ‘Bang! Bang! Bang! Explosively Large Numbers’

### 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’

### Adjoints of Vector Operators

Published January 23, 2020 Occasional Leave a CommentTags: Algebra, Analysis

We take a fresh look at the vector differential operators grad, div and curl. There are many vector identities relating these. In particular, there are two combinations that always yield zero results:

**Question: Is there a connection between these identities?**

### Some Fundamental Theorems of Maths

Published October 24, 2019 Occasional Leave a CommentTags: Algebra, Analysis, Geometry

*Every branch of mathematics has key results that are so
important that they are dubbed fundamental theorems.*

The customary view of mathematical research is that of establishing the truth of propositions or theorems by rigorous deduction from axioms and definitions. Mathematics is founded upon axioms, basic assumptions that are taken as true. Logical reasoning is then used to deduce the consequences of those axioms with each major result designated as a theorem.

As each new theorem is proved, it provides a basis for the establishment of further results. The most important and fruitful theorem in each area of maths is often named as the *fundamental theorem* of that area. Thus, we have the fundamental theorems of arithmetic, algebra and so on. For example, the fundamental theorem of calculus gives the relationship between differential calculus and integral calculus.

### The Brief and Tragic Life of Évariste Galois

Published August 15, 2019 Irish Times Leave a CommentTags: Algebra, Group Theory, History

On the morning of 30 May 1832 a young man stood twenty-five paces from his friend. Both men fired, but only one pistol was loaded. Évariste Galois, a twenty year old mathematical genius, fell to the ground. The cause of Galois’s death is veiled in mystery and speculation. Whether both men loved the same woman or had irreconcilable political differences is unclear. But Galois was abandoned, mortally wounded, on the duelling ground at Gentilly, just south of Paris. By noon the next day he was dead [TM169 or search for “Galois” at irishtimes.com].

Continue reading ‘The Brief and Tragic Life of Évariste Galois’

### The Many Modern Uses of Quaternions

Published October 4, 2018 Irish Times 2 CommentsTags: Algebra, Hamilton

The story of William Rowan Hamilton’s discovery of new four-dimensional numbers called quaternions is familiar. The solution of a problem that had bothered him for years occurred to him in a flash of insight as he walked along the Royal Canal in Dublin. But this Eureka moment did not arise spontaneously: it was the result of years of intense effort. The great French mathematician Henri Poincaré also described how sudden inspiration occurs unexpectedly, but always following a period of concentrated research [TM148, or search for “thatsmaths” at irishtimes.com].

### The Flight of the Bumble Bee

Published August 23, 2018 Occasional Leave a CommentTags: Algebra, Puzzles

Alice and Bob, initially a distance *l* apart, walk towards each other, each at a speed *w*. A bumble bee flies from the nose of one to the nose of the other and back again, repeating this zig-zag flight at speed *f *until Alice and Bob meet. *How far does the bumble bee fly?*

Although polynomial equations have been studied for centuries, even millennia, surprising new results continue to emerge. Marden’s Theorem, published in 1945, is one such — delightful — result.

“It is difficult to imagine modern mathematics without the concept of a Lie group.” (Ioan James, 2002).

Sophus Lie grew up in the town of Moss, south of Oslo. He was a powerful man, tall and strong with a booming voice and imposing presence. He was an accomplished sportsman, most notably in gymnastics. It was no hardship for Lie to walk the 60 km from Oslo to Moss at the weekend to visit his parents. At school, Lie was a good all-rounder, though his mathematics teacher, Ludvig Sylow, a pioneer of group theory, did not suspect his great potential or anticipate his remarkable achievements in that field.

### Cubic Skulduggery & Intrigue

Published March 15, 2018 Irish Times Leave a CommentTags: Algebra, History

Babylonian mathematicians knew how to solve simple polynomial equations, in which the unknown quantity that we like to call *x *enters in the form of powers, that is, *x* multiplied repeatedly by itself. When only *x* appears, we have a linear equation. If *x*-squared enters, we have a quadratic. The third power of *x* yields a cubic equation, the fourth power a quartic and so on [TM135 or search for “thatsmaths” at irishtimes.com].

### Metallic Means

Published February 9, 2017 Occasional Leave a CommentTags: Algebra, Arithmetic, Recreational Maths

with the value

.

There is no doubt that is significant in many biological contexts and has also been an inspiration for artists. Called the *Divine Proportion*, it was described in a book of that name by Luca Pacioli, a contemporary and friend of Leonardo da Vinci.

### The Beginning of Modern Mathematics

Published January 26, 2017 Occasional Leave a CommentTags: Algebra, History

The late fifteenth century was an exciting time in Europe. Western civilization woke with a start after the slumbers of the medieval age. Johannes Gutenberg’s printing press arrived in 1450 and changed everything. Universities in Bologna, Oxford, Salamanca, Paris and elsewhere began to flourish. Leonardo da Vinci was in his prime and Christopher Columbus was discovering a new world.

### Raphael Bombelli’s Psychedelic Leap

Published December 8, 2016 Occasional Leave a CommentTags: Algebra, History

The story of how Italian Renaissance mathematicians solved cubic equations has elements of skullduggery and intrigue. The method originally found by Scipione del Ferro and independently by Tartaglia, was published by Girolamo Cardano in 1545 in his book *Ars Magna*. The method, often called Cardano’s method, gives the solution of a depressed cubic equation *t*^{3}* + p t + q = *0. The general cubic equation can be reduced to this form by a simple linear transformation of the dependent variable. The solution is given by

Cardano assumed that the discriminant Δ = ( *q */ 2 )^{2} + ( *p */ 3 )^{3}, the quantity appearing under the square-root sign, was positive.

Raphael Bombelli made the psychedelic leap that Cardano could not make. He realised that Cardano’s formula would still give a solution when the discriminant was negative, provided that the square roots of negative quantities were manipulated in the correct manner. He was thus the first to properly handle complex numbers and apply them with effect.

### Andrew Wiles wins 2016 Abel Prize

Published May 19, 2016 Irish Times Leave a CommentTags: Algebra, Number Theory

A recent post described the Abel Prize, effectively the Nobel Prize for Mathematics, and promised a further post when the 2016 winner was announced. This is the follow-up post [also at TM091, or search for “thatsmaths” at irishtimes.com].

Next Tuesday, HRH Crown Prince Haakon will present the Abel Medal to Sir Andrew Wiles at a ceremony in Oslo. The Abel Prize, comparable to a Nobel Prize, is awarded for outstanding work in mathematics. Wiles has won the award for his “stunning proof of Fermat’s Last Theorem” with his research “opening a new era in number theory”. Wiles’ proof made international headlines in 1994 when he cracked one of the most famous and long-standing unsolved problems in mathematics.

Pierre de Fermat, a French lawyer and amateur mathematician, stated the theorem in 1637, writing in the margin of a maths book that he had “a truly marvellous proof”. But for more than 350 years no proof was found despite the efforts of many of the most brilliant mathematicians.

### James Joseph Sylvester

Published September 3, 2015 Irish Times Leave a CommentTags: Algebra, History

James Joseph Sylvester was born in London to Jewish parents in 1814, just 201 years ago today. The family name was Joseph but, for reasons unclear, Sylvester – the name of an anti-Semitic Pope from the Roman period – was adopted later. [TM075; or search for “thatsmaths” at irishtimes.com ]

Sylvester’s mathematical talents became evident at an early age. He entered Cambridge in 1831, aged just seventeen and came second in the notorious examinations known as the Mathematical Tripos; the man who beat him achieved nothing further in mathematics!

In the seventeenth century, the algebraic approach to geometry proved to be enormously fruitful. When René Descartes (1596-1650) developed coordinate geometry, the study of equations (algebra) and shapes (geometry) became inextricably interlinked. The move towards greater abstraction can make mathematics appear more abstruse and impenetrable, but it brings greater clarity and power, and can lead to surprising unifications.

### Emmy Noether’s beautiful theorem

Published June 18, 2015 Irish Times Leave a CommentTags: Algebra, Mechanics

The number of women who have excelled in mathematics is lamentably small. Many reasons may be given, foremost being that the rules of society well into the twentieth century debarred women from any leading role in mathematics and indeed in science. But a handful of women broke through the gender barrier and made major contributions. [TM070: search for “thatsmaths” at irishtimes.com ]

Continue reading ‘Emmy Noether’s beautiful theorem’### Mode-S: Aircraft Data improves Weather Forecasts

Published April 2, 2015 Irish Times Leave a CommentTags: Algebra, Geometry, Geophysics

A simple application of vectors yields valuable new wind observations for weather forecasting [see this week’s *That’s Maths* column (TM065) or search for “thatsmaths” at irishtimes.com].

Continue reading ‘Mode-S: Aircraft Data improves Weather Forecasts’

### The Klein 4-Group

Published February 12, 2015 Occasional Leave a CommentTags: Algebra, Group Theory

What is the common factor linking book-flips, solitaire, twelve-tone music and the solution of quartic equations? Answer: .

**Symmetries of a Book — or a Brick**

### The Steiner Minimal Tree

Published January 29, 2015 Occasional Leave a CommentTags: Algebra, Algorithms, Gauss, Maps, Topology

Steiner’s minimal tree problem is this: **Find the shortest possible network interconnecting a set of points in the Euclidean plane.** If the points are linked directly to each other by straight line segments, we obtain the *minimal spanning tree*. But Steiner’s problem allows for additional points – now called Steiner points – to be added to the network, yielding *Steiner’s minimal tree*. This generally results in a reduction of the overall length of the network.

### Old Octonions may rule the World

Published October 16, 2014 Irish Times Leave a CommentTags: Algebra, Hamilton, Number Theory

This week’s *That’s Maths* column in *The Irish Times* (TM055, or search for “thatsmaths” at irishtimes.com) is about octonions, new numbers discovered by John T Graves, a friend of William Rowan Hamilton.

### Algebra in the Golden Age

Published October 2, 2014 Irish Times Leave a CommentTags: Algebra, History

This week’s *That’s Maths* column in *The Irish Times* (TM054, or search for “thatsmaths” at irishtimes.com) is about the emergence of algebra in the Golden Age of Islam. The Chester Beatty Library in Dublin has several thousand Arabic manuscripts, many on mathematics and science.

### Cartoon Curves

Published September 11, 2014 Occasional Leave a CommentTags: Algebra, Computer Science, Geometry, Recreational Maths

The powerful and versatile computational software program called Mathematica is widely used in science, engineering and mathematics. There is a related system called Wolfram Alpha, a computational knowledge engine, that can do Mathematica calculations and that runs on an iPad.

### The High-Power Hypar

Published May 29, 2014 Occasional Leave a CommentTags: Algebra, Gauss, Geometry, Recreational Maths

Maths frequently shows us surprising and illuminating connections between physical systems that are not obviously related: the analysis of one system often turns out to be ideally suited for describing another. To illustrate this, we will show how a surface in three dimensional space — the hyperbolic paraboloid, or *hypar* — pops up in unexpected ways and in many different contexts.

### The Unity of Mathematics

Published March 20, 2014 Irish Times Leave a CommentTags: Algebra, Analysis, Geometry, Number Theory

This week, *That’s Maths* in *The Irish Times* ( TM041 ) is about an ambitious program to unify mathematics.

Mathematics expands! Results once proven to be true remain forever true. They are not displaced by subsequent results, but absorbed in an ever-growing theoretical web. Thus, it is increasingly difficult for any individual mathematician to have a comprehensive understanding of even a single field of mathematics: the web of knowledge grows so fast that no-one can master it all.

### The Langlands Program

Published March 13, 2014 Occasional Leave a CommentTags: Algebra, Analysis, Arithmetic, Group Theory, Number Theory

An ambitious programme to unify disparate areas of mathematics was set out some fifty years ago by Robert Langlands of the Institute for Advanced Study in Princeton. The “Langlands Program” (LP) is a set of deep conjectures that attempt to build bridges between certain algebraic and analytical objects.

### Speed Cubing & Group Theory

Published February 13, 2014 Irish Times Leave a CommentTags: Algebra, Algorithms, Group Theory, Puzzles

The article in this week’s *That’s Maths* column in the* Irish Times* ( TM038 ) is about Rubik’s Cube and the Group Theory that underlies its solution.

Two lines in a plane intersect at one point, a line cuts a circle at two points, a cubic (an S-shaped curve) crosses the *x*-axis three times and two ellipses, one tall and one squat, intersect in four places.

### The Watermelon Puzzle

Published November 14, 2013 Occasional Leave a CommentTags: Algebra, Puzzles, Recreational Maths

An amusing puzzle appears in a recent book by John A. Adam (2013). The answer is very surprising. The book argues in terms of simultaneous equations. A simpler argument, using the diagram below, should make all clear. Continue reading ‘The Watermelon Puzzle’

The *That’s Maths* column in the* Irish Times* this week is about symmetry and group theory, and the possible link, through string theory, with the fundamental structure of the universe ( TM020 ).

In the arts, symmetry is intimately associated with aesthetic appeal. In science, it provides insight into the properties of physical systems.

### 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’

**This week’s That’s Maths article, at TM002, describes how Google’s PageRank software finds all those links when you enter a search word, by solving an enormous problem in linear algebra.**

**A comprehensive description of PageRank is given in the book Google’s PageRank and Beyond: The Science of Search Engine Rankings, by Amy N. Langville & Carl D. Meyer This book won an AAP Award in 2006 for Best Professional/Scholarly Book in Computer & Information Science.**

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