In keeping with Carnival tradition, I’m compelled to inform you that, while it’s generally not particularly interesting:

- 174 is an abundant number, meaning if you write down all its proper divisors and add them together, the total is more than 174. It’s quite factor-y.
- It’s also an odious number, which means it has an odd number of ones in its binary representation (as opposed to being an evil number, with an even number of ones).
- It is also a 59-gonal number – which means that 174 things can be arranged into a 59-sided shape. Play more with polygonal numbers here.

Now, on to the Carnival!

If you enjoyed our Big Internet Math-Off here this summer, you might find it nice to know that one of the Math-Off entries has inspired a knitted piece from Pat & Steve over at Woolly Thoughts.

Regular Carnival host Kartik has noticed an interesting pattern in the way the trees look while driving down the highway, and discovered an interesting number-theoretic reason behind it.

Over on Medium, Digya Acharya has put together a nice introduction to one of my favourite topics, information theory, and an intuitive introduction to linear regression.

Meanwhile, at the European Mathematical Society’s blog Mathematics in Europe, Gianluigi Filippelli shares the curiosity that is lunar arithmetic.

Ari Rubinsztejn has shared an in-depth response (including numerical simulations) to a maths problem posed on Twitter by YouTuber Primer, which involves throwing coloured balls into bins.

While many of our Carnival entries are simple blog posts, some go the extra mile. Nan Ma has built a website to visualise regular star polytopes in 2D, 3D, and 4D, and if you’re a fan of 3D shapes, there’s a wealth of images, animations and explanations to explore.

While we’re on Serious Business, Math Vault have shared their Definitive, Non-Technical Introduction to LaTeX, Professional Typesetting and Scientific Publishing – it explains what different typesetting options you have and why LaTeX is clearly the best one.

And finally, Carnival regular hosts Ganit Charcha have started a mathematics magazine – and they’re looking for reader submissions. It’s aimed at K-12 students (ages around 5-18) and submissions from students are welcome – so if you know any students who might like somewhere to write for, point them that way!

*The next Carnival of Maths will be #175, and when it lands we’ll post a link here. If you’d like to host a future Carnival, you’d be very welcome – visit our **Carnival of Maths page** for more info.*

*Barcelona-based publishing company Kronecker Wallis have produced a new updated edition of Byrne’s Euclid. We asked founder and editor Jordi Anton to tell us all about it – and their related Principia reprint, which is still looking for funding on Kickstarter.*

**Tell us about Euclid’s Elements.**

Euclid of Alexandria lived c. 300 BCE. He wrote The Elements, the most widely used mathematics and geometry textbook in history. The Elements consists of thirteen books. In all, it contains 465 theorems and proofs, described in a clear, logical and elegant style, and using only a compass and a straight edge. Euclid’s Elements has influenced all branches of science but none so much as mathematics and the exact sciences. No other book except the Bible has been so widely translated and circulated.

The first printed version of the Elements appeared in 1482 with the advent of the printing press. It was based on Campanus of Novara’s 1260 edition. On May 25, 1482 printer Erhard Ratdolt of Venice issued the first printed edition of Euclid’s Elements. It was the first substantial book to contain geometrical figures. From definitions and axioms, Euclid showed how to prove dozens of mathematical propositions, producing knowledge that was objective and undeniable.

Isaac Newton’s famous work Principia Mathematica clearly demonstrates Euclid’s influence. Newton called his famous laws of motion “axioms” and deduced his law of gravitation in the form of two mathematical theorems.

Irish-born Oliver Byrne (1810-1880) was an innovator in mathematics education, particularly in the teaching of geometry. His most well-known book was his colorful version of ‘Euclid’s Elements’, published in 1847. Oliver Byrne employed a red, yellow, and blue color scheme for the figures and diagrams in his most unusual 1847 edition of Euclid’s Elements.

“I do not introduce colours for the purpose of entertainment, or to amuse by certain combinations of tint and form, but to assist the mind in its researches after truth, to increase the facilities of instruction, and to diffuse permanent knowledge”.

Oliver Byrne

Byrne had experimented with colors in schools and he had evidently decided that the schoolteacher’s approach indicating lines, angles,… on the blackboard and then making deductions from them would be better described by his method than in the usual way.

Oliver Byrne’s 1847 Euclid was one of the first multicolor printed books. Many consider it the most attractive edition of Euclid’s Elements ever produced.Byrne’s Euclid was exhibited in London at the Great Exhibition of 1851. Praise was given for its beauty and the artistry of the printing, which may have influenced future publications and artwork.

After printing Isaac Newton’s Principia, we were searching for another major book in science. We have been in love with Elements for a long time and as design enthusiasts, Byrne’s work held a special place in our minds. Those beautiful, minimalist, clean and didactical lines encouraged us to start a crazy adventure, to finish Byrne’s work. All 13 books.

It simply could not be unfinished!

The first six books are identical. We only applied a modern vectorial design to graphs and a new typography, but the content is the same. Our hard work started when creating the visual interpretation of the rest of the books, from 7 to 13.

A team of 6 mathematicians worked almost a year and a half – thinking, drawing and writing every page of the books. The team not only have great mathematical skills, but also a deep knowledge of mathematics history and mathematics didactic.

Absolutely. Almost all the later books were a challenge, especially the 10th. This book involved a very long journey for our mathematicians. Not only talking about maths – the entire project was a challenge because we needed to manage a large team of mathematicians, designers, editors… taking our small company nearly to its limits – it was hard and difficult to adapt a lot of non-geometrical propositions; lots of points-of-view, a lot of nights thinking how to solve a problem… but in the end we have achieved what we believe to be an outstanding end result.

We were faithful to Byrne’s philosophy and before any designer started to work, we created a visual guide for internal use. With that guide, we worked together with mathematicians re-using graphical elements and creating some new ones – because books 7 – 13 needed a new color (some graphs needed more than Byrne’s three basic colors).But focusing on your question, for the less visual content, we followed Byrne’s color scheme and put it into the text as imaginary words.

We are intrinsically ‘digital’ and know that physical books nowadays can seem hard to manage and expensive….thats the reason we print books with high quality papers and with a love for design. We try to keep an eye on the details and quality. We have a high respect for our customers and want to create books that meet their expectations (when they are committed to not relying on the free digital versions) – it’s our priority. Obviously, our Elements is an expensive book because it was very expensive to produce. Much more than our other books.

We smiled when we found out that Byrne’s Euclid was extremely difficult and expensive to produce. Only one thousand copies (almost like our crowdfunding campaign) were originally published. It was sold at a price of 25 shillings, almost five times the typical book price at the time. Maybe we are also close to that ‘five times the amount’ with our book – compared to a typical book.

Our audience are science lovers. A lot of our customers send us ideas of new books, authors,… and they are science people. But also they love well-produced books and buy them as collectors because our books are books to own, not only to read. We do not know how to, nor do we want to, create a monotonous and characterless product. We want to create books to own and create the desire to touch unique books made by lovers of books and science. Not only for customers.

Patience! We published it with a few delays because we prioritized quality and good content versus speed. That meant, people had to have a lot of patience with us waiting for their books without asking. We love our customers and supporters, they are the most important motivation for us.

Also, we learned how beautiful mathematics can be and the power of joining mathematics and design – to reach more people and understand math better.

Yes! Posters – we created a poster of every book cover. The cover design is our creation, Byrne didn’t create them. They are truly beautiful.

At the other hand, our **Newton’s Principia** could be also a related product. Newton used Euclid’s Elements knowledge and language to introduce his theorems. Since last Tuesday we are trying to reprint it again.

**What’s your next project? Is it also maths-related?**

Now we are only focused on a 6-book Astronomy collection. We did a Kickstarter campaign earlier this year, and we are working hard now on translations. Another challenge for us!

We don’t know which will be our next big project. I’ll keep you posted!

]]>People We Know Who Are Great

**Matt Parker: Humble Pi**

Pleasance Dome (10 Dome), 8.20pm (1h) 16+, 2-26 Aug £12.50 (previews 31 Jul-1 Aug £7.50)

Aperiodipal and stand-up mathematician Matt Parker brings the show of his latest book (of the same name) to Edinburgh, sharing his favourite mathematical mistakes, from misplaced decimal points to combinatorial calamities – and the results, which vary from amusing to pretty serious. Truly a comedy of errors.

**Maths Madness with Kyle D Evans**

PBH’s Free Fringe @ Bar Bados (Room 7), 12pm (1h) 8+, 3-12 Aug (free, donation optional)

When he’s not teaching maths, superfriend of the site and 2019 Math-Off competitor Kyle D Evans is well known for playing mathematical songs on his guitar. For the Fringe, Kyle presents a family show containing stacks of audience participation and some mind-bending mathematical concepts.

**Timandra Harkness: Take a Risk**

Assembly Roxy (Downstairs), 11.15am (1h) 12+, 2-26 Aug £10 (previews 31 Jul-1 Aug £6)

Having previously brought an engineering comedy show, a neuroscience comedy show, and a comedy show about the mathematics of death, Timandra’s Fringe shows are a must for anyone mathematically minded. This time she’s aiming a probably not loaded pistol at the idea of risk, in a show that includes graphs and gambling, songs, jokes and electric shocks.

**Foxdog Studios: Tomorrow’s Office**

Heroes @ The Hive (The Big Cave), 5pm (1h) 18+, 1-25 Aug £5

IT rock ‘n’ roll superstars and Festival of the Spoken Nerd regular guests FoxDog Studios bring their latest inventions to share, including a musical mop, a souped-up sausage cannon and a pair of light-up bongo boots. Bring your phone to join in the fun.

**Morgan & West: Unbelievable Science**

Assembly George Square (Gordon Aikman Theatre), 4.30pm (1h) 5+ (5-14), 2-25 Aug (not 21) £12.50 (previews 31 Jul-1 Aug £8)

Unbelievable Science is an interactive science show for the whole family, with live magical experiments. Magicians, time-travellers and all-round spiffing chaps Morgan & West secretly used to be proper scientists (I can also verify they’ve been known to maths occasionally), and now they’re bringing their knowledge to the stage.

**Harry Baker: I am 10,000**

Underbelly, Cowgate (Belly Laugh), 11.40am (1h) 8+, 1-24 Aug £11 (previews £6.50)

Mathematician-turned-World-Slam-Champion Harry Baker turns 10,000 days old, celebrating numbers, words and life itself. From winning his school’s Battle of the Bands competition with a Jay-Z maths homage, to his prime number poetry TED talk being watched by millions online, Harry’s love of language and logic has got him through literal marathons, seen him rap battle in front of Ice Cube, and now has him analysing the technical accuracy of So Solid Crew’s 21 seconds. He’s got 99 problems but maths ain’t one.

**Tom Cashman: XYZ**

Underbelly Bristo Square (Clover), 8.10pm (1h) 16+, 2-25 Aug (not 13) £11.50 (previews 31 Jul-1 Aug £6.50)

Australian comedian Tom Cashman is bringing his latest stand-up show XYZ to the Fringe. It’s about maths, Italians and estate agents. Tom’s had a huge year – writing and featuring on the ABC’s Tonightly in Australia, until it was cancelled by the government for being too funny.

**Blindingly Obvious**

C Venues – C Cubed (Main Space), 9pm (50 mins) 12+, 1-26 Aug (not 13) £10.50

After an exciting year of nationwide festival debuts, Richard Wheatley returns to where it all began one year ago. Funny, fast and friendly, Richard mixes anecdotes from his unique life with off-the-cuff audience interactions for high energy hilarity. An hour with Britain’s funniest friendliest blind theoretical physicist turned award-winning radio newsreader and stand-up comedian is never dull, especially when he promises to keep the maths jokes to a minimum.

Outside of the stand-up circuit, you might find yourself interested in this Introduction to Paper Folding workshop (White Stuff, 2nd floor workshop space, 1.30pm (2.5h), 18 & 21 Aug, £40). There’s also The Maths Magic Show (PBH’s Free Fringe @ CC Blooms (Venue 171), 12.30pm (55 mins) 8+, 3-25 Aug, free (donation optional)) featuring Jason Davison – a mathematical magician (mathemagician) who’s featured in some of the videos at the excellent mathematicalmagic.com – which promises some magic tricks to show your friends and an exciting new perspective on maths.

If you’re a fan of puzzles, I can personally recommend the Agent November Escape room games (31 Jul-25 Aug, The Stand’s New Town Theatre (Committee Room), various times 8+, £15) – hefted up from their usual home in London for the month, and with three different games to keep you busy (Major X Ploe Shun, Robyn Yew, and Murder Mr E).

]]>- Public Key Cryptography (29 January) in which I describe the famous work of HLF regulars Diffie and Hellman
- A puzzle ‘four’ the new year (11 January) in which I discuss number puzzles, which do and don’t involve the digits 2, 0, 1 and 9
- The Twelve Facts of Christmas: Pascal’s Triangle (20 December), a festive round-up of mathematical facts
- Right on the Money (4 December) in which I wonder if the new British £50 will have a mathematician on it
- Measuring the Change (21 November) on the forthcoming redefinition of the kilogram
- Permutations and Tribulations (13 November) on the superpermutations discovery made anonymously on the internet
- Katherine Johnson (7 September) on life of the mathematician
- Game, SET and maths (16 August) about the card game SET
- New shape discovered – right under your nose (6 August) in which I describe the newly-discovered scutoid shape, found in nose cells
- Flexagons and false advertising (27 July) in which I explain how ordinary paper can be much more impressive if you flex it, Martin Gardner-style
- Few tile attempts (5 July) in which I discuss tilings and tessellations, and then decide how to redecorate my bathroom
- Cake and Coincidence (21 June) in which a striking coincidence prompts a discussion on probability and birthdays
- The Bridges of Königsberg (29 May) discussing the famous problem in graph theory
- A truly special occasion (18 May) all about myself and my partner’s Golden (ratio) wedding anniversary
- Colouring in like a mathematician (3 May) covering the then-current Chromatic Number discovery

I’ll continue writing posts for HLF’s Spektrum blog as long as they want me to – keep checking their Twitter feed or the blog’s RSS feed to see them as they appear!

]]>Our official list of #Noethember facts has provided inspiration for many. We’ve of course had daily sketches from our ‘ring’-leader @Coni777 – who’s also shared some photos of the drawing process:

The making of #noethember day 1. Greetings from France!! pic.twitter.com/L6fifvVRBf

— Constanza Rojas-Molina (@Coni777) November 1, 2018

Beautiful fox-based illustrations from @Lele_Saa:

Excited to take part on #Noethember, this month's drawing challenge about Emmy Noether, the mathematician, designed by @Coni777 @aperiodical https://t.co/5QY38BMg3E pic.twitter.com/2FpwtwfUmD

— Lele Saa (@Lele_Saa) November 1, 2018

Pencil and biro sketches from @njj4 and @tkleinwalsh:

Amalie Emmy Noether. Born 23 March 1882 in Erlangen, daughter and eldest child of Max Noether and Ida Amalia Kaufmann. Max, a mathematician, worked on algebraic geometry. #noethember pic.twitter.com/h4bapYtdtu

— Dr Nicholas Jackson (@njj4) November 1, 2018

Emmy decided to attend university in 1900. Then she spent three years independently preparing for the entrance exam. NBD. #Noethember pic.twitter.com/ZwQgVXqS2f

— Tina Klein Walsh (@tkleinwalsh) November 6, 2018

Others have used the idea as a springboard to collect their own ideas, including @mathsbooks, who has compiled their own list to work from and used multiple media, including sketches, watercolours and collage; and @algebrasnotwar who’s been drawing lovely cartoons.

#Noethember my day 14: After their legendary walking tours, @uniGoettingen’s mathematicians enjoyed Emmy Noether's yummy „Pudding à la Noether“. They continued their maths conversation, which became known as „Pudding Seminars“.https://t.co/wxFbSc1P7Z pic.twitter.com/sBStkVpd7H

— Katharina H MathsBooks (@MathsBooks) November 14, 2018

My #Noethember so far. 10 of 30 – the first third.

In contrast to the contributions of the other #Noethember enthusiasts, my amateurish attempts occur as quite a jumbled mess of styles with no recognition value. pic.twitter.com/D1hwBtRvHP— Katharina H MathsBooks (@MathsBooks) November 11, 2018

Noether was invited to return to the University of Göttingen by David Hilbert and Felix Klein#noethember pic.twitter.com/5fJErE4mdF

— Robert Vandermolen (@algebrasnotwar) November 12, 2018

The project has been a chance for people to join in even if it’s not a daily commitment, and many have shared occasional images without posting every day, including myself (@stecks), @gravitywithhat and @christianp. Others are joining in with a single post – and it’s all good!

#noethember day 8 pic.twitter.com/XOnoqOLwGQ

— Christian Lawson-Perfect (@christianp) November 8, 2018

https://twitter.com/GravityWithHat/status/1062395396180328449

@aperiodical #Noethember Day 2: See Emily Play pic.twitter.com/tTgm4Fnoc5

— Soup Dragon (@soupie66) November 2, 2018

Charmed to learn that mathematicians are celebrating #Noethember this month in celebration of Emmy Noether with facts and #sciart! My portrait of her focuses on her impact on #physics – Noether’s theorem links symmetries and conservation laws, for exampl… https://t.co/dL5lmGBOe0 pic.twitter.com/Dk06OiQQNn

— Dr Ele Willoughby (@minouette) November 14, 2018

#noethember Emily applied to the Universitynof Erlangen to first observe mathematics lectures there.she could only do that because women where not allowed to enroll at the University @Coni777 pic.twitter.com/KKw6KfIfiH

— Andrea Troncoso (@aitroncoso) November 9, 2018

"Your work has changed the way we look at algebra, . . . you have left your name written indelibly across its pages . . . we will always cherish the legacy you left us" -Hermann Weyl #noethember pic.twitter.com/1B8YSHnz1b

— Rachel Quinlan (@rkquinlan) November 12, 2018

#noethember pic.twitter.com/WbpJEqyosj

— imperatrixmundi (@o_fortuna) November 9, 2018

Others are using the hashtag to share other types of Noether-related content – from archive photos and documents to videos and books.

Emily Noether's dismissal letter from Gottingen 1933. She along with every other Jewish Professor was barred from teaching. Unlike many contemporaries she luckily managed to escape the Nazis. #noethember pic.twitter.com/4zohKwOt6K

— Benjamin Leis (@benjamin_leis) November 13, 2018

#Noethember Letter by Emmy Noether to David Hilbert. Erlangen, 1 December 1914, digitized version via @subugoe: https://t.co/SZfbSu8i24 pic.twitter.com/4VjnG4bxXK

— Katharina H MathsBooks (@MathsBooks) November 9, 2018

#Noethember En 1932, Emmy Noether est la 1ère femme invitée à donner une conférence plénière au congrès international des mathématiciens, qui se tient à Zürich.

L'occasion de jouer au célèbre jeu "Où est Emmy ?" (bien qu'il ne doit pas garanti qu'elle soit sur la photo). pic.twitter.com/eirce5Wumq

— Albireo (@foretdesciences) November 14, 2018

Emmy Noether, une femme extraordinaire à découvrir. Il y a 100 ans, elle a publié un théorème très important qualifié de "monument de la pensée mathématique" par Albert Einstein.

Avec une magnifique miniature de Maïm Garnier.@maybeegreen #noethember https://t.co/6IR2JLNJD2— Scienticfiz (@Vidosscientifi1) November 14, 2018

A l'initiative de @Coni777, consacrons ce mois de novembre à Emmy Noether: #noethember

La couverture de ses œuvres choisies. pic.twitter.com/l7chTJdfmO

— Roger Mansuy (@roger_mansuy) November 10, 2018

#Noethember Letter by Emmy Noether to David Hilbert. Erlangen, 1 December 1914, digitized version via @subugoe: https://t.co/SZfbSu8i24 pic.twitter.com/4VjnG4bxXK

— Katharina H MathsBooks (@MathsBooks) November 9, 2018

Emmy Noether utilisait même les cartes postales pour parler mathématiques.#noethember @Coni777 @roger_mansuy @paljasn @GavageSylvie @mickaellaunay pic.twitter.com/cnODXTCfmo

— Scienticfiz (@Vidosscientifi1) November 3, 2018

There’s still half a month to go – remember, just because you haven’t drawn something every day so far, or if you’ve started and lapsed (like me… just too busy!) doesn’t mean you can’t join in now. And you don’t have to be amazing at drawing – it’s all about sharing ideas and stories. Join the #Noethember movement!

]]>However, since the Nerds are currently riding an exponential curve of silliness in their DVD release schedule (their last show Just for Graphs was released on VHS as well as DVD) this time the show has been released as an autographed limited edition set of 3.5″ floppy disks, one of which was sent to me in the post.

Each of the disks contains one 30-second segment of the show, and I’ve been sent disk number #211, containing seconds 6300 through to 6330 of science comedy content. I was apprehensive, as I know there are many different parts to the show, and I was hoping for one with some mathematical content that our Aperiodical readers here could really appreciate.

Probabilistically, this wasn’t much of a worry – even though the show covers a range of topics, there’s plenty of maths behind all of them. Singer and physicist Helen includes a song about the relative radioactive exposure from different daily activities, each given in terms of in the Banana Equivalent Dose (the amount of radioactivity you’re exposed to from eating a banana), while experiments guy Steve takes a break from exploding things to tell us about his attempts to find meaning in the sentence “the temperature outside a plane is six times colder than the temperature inside a freezer”, a struggle long-term Aperiodical readers will be familiar with, and Steve’s initial response to which is now immortalised in t-shirt form.

The show also contains a wonderful thread of purely maths content from in-house number ninja Matt Parker, who tells us of his campaign to rid the UK’s signage of geometrically inaccurate football symbols – just one of a range of bits on geometrical topics: from his struggles tiling his own bathroom, to playing with stereographic projections and spherical camera footage.

The 30-second clip on my disk is from a section on recursive spirals, inspired by the MC Escher lithograph of a person looking at a painting of a city in which there’s an art gallery through the window of which can be seen that same person, and in the show Matt takes this idea and runs with it… maybe slightly too far.

My impression of this 30-second clip was that it was a little out of context and could have done with a better explanation to introduce what Matt was talking about (he also seemed to just start talking mid-sentence, and didn’t really round off what he was saying at the end of the clip either – it’s a bit of a cliffhanger); we also didn’t get to see much of Steve or Helen, apart from them being over on the left of the stage listening to Matt.

You’ll be pleased to hear that each floppy disk edition also comes with a code to download and watch the whole show, not just the 30 seconds on the disk. It can be ordered from the FOTSN online shop, along with a version of the show on DVD for normal people, which includes a ‘safer for schools’ soundtrack, behind-the-scenes DVD extras and an infinitely long DVD unboxing video extra (of course). There’s also a standalone download edition, for if you don’t want to be encumbered by messy real-world objects – or if, like the nerds themselves, you prefer the purity of buying just the ones and zeroes.

]]>Earlier this year, one of our colleagues made an interesting observation about the Wikiquote page for Mathematics . Wikiquote collects interesting and pithy statements, with references, and categorises them by subject. What our friend Colin had noticed that was almost all of the quotes on the page about mathematics were from men.

This reflects on existing gender imbalance in mathematics, which will hopefully improve. But mathematics is done by all kinds of people all over the world, and many of them have occasion to say interesting and/or profound things about their subject – even the ones who aren’t men. Since Wikiquote is part of the Wikimedia network and can be edited and contributed to, we held a small editing day back in May where we added a number of quotes from female mathematicians to the page, to try to balance out the score.

Walking around the Women in Mathematics featured here at the HLF this week, I was featured by the amazing quotes taken from the interviews with each of the mathematicians. I’ve picked some of my favorites – and yes, I’ve added them to the Wikiquote page . Enjoy!

“In doing mathematics, I express something personal. It is a source of joy to know that, despite this personal aspect, the fruit of my work can be of interest to other mathematicians. “- **Nalini Anantharaman**

“Mathematics offers a common language across borders. It’s a real joy. “- **Alice Fialowski**

“My earliest mathematical memory is my father’s explanation of the theorem that three angles in a triangle add up to 180 degrees. The idea that something could have proved to be true was very appealing to me. “- **Frances Kirwan**

“I used to fear I was on the right track. You need to develop a personal conviction that you *are a mathematician* , and that’s what you are doing. “- **Katarzyna Rejzner**

“I enjoy being surprised by mathematics and its intrinsic difficulty. The moment I enjoy the fall of one coherent whole. “- **Katrin Wendland**

“You should not choose to do mathematics if you want to make money; your salary as a mathematician will never correspond to the amount of time invested in your work. “- **Margarida Mendes Lopes
**

“I like to find out as much as I can about a mathematical object as possible, just as you would like to understand a person as well as possible.” – **Oksana Yakimova**

For the Wednesday afternoon of HLF, the entire conference gets on a (very large) boat and heads off for a gentle cruise down the river, drink in hand and ready to enjoy the scenery. The young researchers, along with the Laureates and the rest of us, are effectively trapped on the boat for a few hours – so just like last year, we took the opportunity to corner some of the PhD and postgrad students and ask them about their research – and the numbers they find central to their work.

*Mathematician, Functional Analysis*

Becky’s research is in pure mathematics, working with objects known as *C*-algebras* – originally developed to provide a mathematical framework for quantum physics. Using cohomological data, she ‘twists’ these algebras with 2-cocycles (giving the 2 Becky chose as the number to represent her work), and studies how this changes the fundamental properties of the objects, such as *commutativity* – whether two operations give the same result if performed in either order. This contributes to an overall effort to completely classify C*-algebras.

*Computer Scientist, Medical monitoring*

Edward is working on a system that can monitor haemoglobin levels in a person’s blood, using only the camera and flash in an everyday smartphone camera. Putting your finger over the camera lens, the system can see the colour of the blood each time a heartbeat pushes it through the fingertip. Using devices that are already prevalent brings obvious advantages in terms of cost and ease of distribution. The number Edward is most familiar with is the resting heart rate of his most frequent test subject – himself.

*Computer Scientist, Hardware Architecture*

Sandhya works in hardware architecture, designing integrated circuits for applications such as machine learning – her research happens somewhere in the overlap between computer science and electrical engineering. To represent her research, Sandhya chose a binary sequence of 0s and 1s, since she works right down at the level of the individual bits shuttling around the hardware. (For the picture, we chose an arbitrary sequence, despite our previous thoughts on this issue.)

*Computer Scientist, Approximation Algorithms*

Eric’s research concerns approximation algorithms – routines for finding good solutions to mathematically difficult optimisation problems (for example the famous ‘Travelling Salesman’ problem). He works specifically with a class of problems computing things known as *submodular functions*. For this class of problems there is a mathematical limit on how well they can be approximated, given by $*1-(\frac{1}{e})$*, or about $0.632$. This forms a kind of ‘holy grail’ for these algorithms, so naturally Eric chose it as his number.

*Computer Scientist, Healthcare Informatics*

Moumita develops machine learning systems, using patient information and electronic health records to predict outcomes like drug interactions, or hospitalisation rates for patients with chronic illnesses. Accurate predictions allow for more effective clinical decision-making, in turn leading to improved outcomes, that is to say, saving lives. Her chosen number – 67% – provides a kind of informal benchmark when assessing these models for possible adoption.

]]>Alongside the HLF this year, an exhibit celebrates female mathematicians from around Europe (written about by Gina in a post earlier this week) and includes photographs, interview quotes and beautiful mathematical equations, which come together to create an illuminating and at times poetic snapshot of the life and work of a mathematician.

The equations in particular caught my eye, each splashed across the poster in a different bright colour. They’re used more as an illustration of the type of maths each person works on, rather than giving any mathematical background – but I was intrigued, and thought I’d investigate a few of them, and share some of the mathematics represented.

Subject area: Cluster algebras, cluster categories, representation theory, categorification

Karin’s work involves **algebras** – structures defined using a basic collection of objects, with an underlying set of numbers used to scale them. An example might be the **complex numbers**, discussed in the post on the Riemann Hypothesis, in which the objects are just the number *i*, and the underlying set is the real numbers. You can combine multiples of $*i$* with real numbers, to get complex numbers of the form $*a + ib$*, and these can be combined by addition, or multiplication to give other complex numbers. Some algebras have more than one object that can be combined in different multiplicities – for example, the **quaternion numbers** are defined in a similar way but using $i, j$ and $k$ – each of which can be multiplied by scalars, but also interact with each other in specified ways (in this case, $i^2 = j^2 = k^2 = ijk = -1$). In particular, Baur’s work is on **Cluster Algebras**, whose collection of objects is generated from a seed set using particular rules.

The equation relates A, an algebra, to End_{B}, which is a collection of endomorphisms. Endomorphisms are maps from a particular object to itself – for example, given the set of numbers {1, 2, 3} you could consider all the maps taking this set to itself, by reordering the numbers:

{1, 2, 3} → {1, 2, 3}

{1, 2, 3} → {1, 3, 2}

{1, 2, 3} → {2, 1, 3}

{1, 2, 3} → {2, 3, 1}

{1, 2, 3} → {3, 1, 2}

{1, 2, 3} → {3, 2, 1}

Once you have defined the endomorphisms of an object, they can then be considered as a structure in themselves. In the same way as with the objects in the algebra, you can combine one endomorphism with another to get a different one:

e.g. {1, 2, 3} → {1, 3, 2} combined with {1, 2, 3} → {2, 1, 3}

This would swap the second and third elements, then swap the first and second elements, giving the result {1, 2, 3} → {3, 1, 2}. Studying all the possible endomorphisms of a given algebraic object tells you something about its structure, and the collection of endomorphisms can also form an object to be studied.

The equation is from Karin’s paper “Dimer Models and Cluster Categories of Grassmannians”, with Alastair King and Robert J. Marsh. In this paper, they show that the particular algebra they are studying, A, is isomorphic to (the same as) a particular endomorphism algebra, giving them a better understanding of its structure.

Subject area: Geometric analysis, minimal surfaces, Dirichlet problem, geometric maximum principle

This equation is from Nelli’s paper, Minimal surfaces in $\mathbb{H}^2 \times \mathbb{R}$, written with Harold Rosenberg, in which they prove various results about the space $\mathbb{H}^2 \times \mathbb{R}$.

$\mathbb{H}^2$ here represents the **hyperbolic plane** – a surface in which the space curves away from itself at every point. This sounds confusing, but it’s difficult to picture as it doesn’t fit in our normal 3D universe. Compared to our usual geometry (called Euclidean geometry), it has major differences. One of the fundamental ideas in geometry is if you have a point near a line, there’s only one line that passes through that point and is parallel to the original line – this is known as Playfair’s axiom. In hyperbolic space, there can be more than one such line – all of which pass through the same point, but don’t intersect each other, or cross the original line, anywhere else. This is because of the way the space is curved, and it’s a fundamental property of so-called Hyperbolic geometry.

Hyperbolic space can be visualised using the **Poincaré Disc** – a circle in which distance behaves strangely near the edges. Distances in the centre of the disc behave just as normal in the regular 2D space we’re used to, but as you get nearer the edges, distances get shorter – until, on the boundary of the disc, points which look close together are actually far apart, and straight lines become curved.

A nice way to think about it is to imagine you’re creating a circular piece of crochet, but each line of stitches as you go further out from the centre has more stitches in it. Such a crochet piece might start off flat, but as you get further out it’ll need to ripple up and down to accommodate the extra stitches – but in the hyperbolic plane, this extra surface is just squashed in to the same space, and the definition of distance is difference there.

The space$\mathbb{H}^2 \times \mathbb{R}$ represents the result of taking the **direct product** of the hyperbolic plane with the real line $\mathbb{R}$. Direct products are analogous to putting two things at right angles – for example, the direct product of a circle and the infinite real line $\mathbb{R}$ is an infinite cylinder, and the direct product of two real lines $(\mathbb{R}$ \times\mathbb{R})$ is $\mathbb{R}^2$, the 2-dimensional real plane.

Nelli’s work here concerns the **Dirichlet Problem**, which involves solving differential equations, and this equation describes the divergence (a property of the related vector field) of a function defined on $\mathbb{H}$^n, n-dimensional hyperbolic space.

Subject area: Algebraic groups and Lie algebras, Poisson structures, harmonic analysis on Gelfand pairs

This equation is known as **Weyl’s character formula**, and it’s from a branch of maths called **representation theory**, which is connected to the idea of **groups** – collections of objects, much like algebras, but without the underlying set of scalars. Group theory is concerned with how the objects making up the group behave when combined in different ways, and group structures often underlie other mathematical ideas – the group describing all possible moves on a Rubik’s cube is a nice example.

Representation theory involves representing elements of a group or other algebraic structure in terms of linear transformations of vector spaces. Results from this common ground can then be used to learn about the original structures. Representation theory often pops up in other areas of research, as the underlying groups the structures are based on show the connections between different areas.

As with numbers and primes, representations can be ‘broken down’ into products of smaller representations (transformations of spaces with fewer dimensions). Those representations which cannot be broken down are called irreducible representations. Much like prime numbers, properties of irreducible representations are particularly important.

The **character of a representation** condenses this further, assigning to elements of the group a single ‘number’ which captures much of the information in the representation. Weyl’s character formula gives information on the characters of the irreducible representations of a certain type of group, known as a compact Lie group. Lie groups, which Oksana works with, are groups that can also be considered as topological shapes.

The HLF included a talk from 2018 Fields medalist Caucher Birkar. His subject area, algebraic geometry, is one of the largest fields of research within pure mathematics (over a quarter of the 60 Fields medals awarded since 1936 have been to people working in algebraic geometry), and it has connections to many other fields of maths including topology, algebra and number theory. But what exactly is algebraic geometry? Well, if you’ve studied maths at school, there’s a pretty good chance you’ve already done some.

Algebraic geometry considers spaces of polynomials – equations which use one or more variables raised to powers. A simple example might be:

$x^3 + 3x^2 – 4x + 5 = 0$

Each of the terms in the polynomial has a coefficient in front of it, which can be 1 (in which case it’s not written), and can be 0 (in which case that term doesn’t appear) or can be another number. Depending on what kind of polynomial you’re working with (more strictly, over which field you’re defining your space of polynomials), you might use whole numbers, fractions or even complex numbers in front of each term. In our example above, there’s an $x^3$ term, an $x^2$ term, an $x$ term (which in this case has a negative coefficient) and a constant term.

This kind of polynomial equation (*poly* = many, *nomos* = part; a thing with many parts) can be used to describe all kinds of systems and objects. Simple example polynomials might not have terms with high powers – for example, a polynomial with just an $x$ term and a constant term is called linear, so-called because it describes a straight line if you draw it on a graph.

This line represents all the points for which $y = 2x + 3$: at $x = 0, y = 3$ and at $x = 1, y = 5$ as you would expect. Many of you will be familiar with this kind of graphical representation of an equation, and might have also seen what happens to the graph of a polynomial as you include higher powers as terms.

A graph with a squared term (left) is a quadratic, and will have a u-shaped (or n-shaped, depending on whether the $x^2$ term has a positive or negative coefficient) curve. A cubic polynomial (centre) will usually have a wiggle in the middle, but will have the ends going in opposite directions, and a polynomial with an $x^4$term (a quartic, right) will look like a quadratic but with an extra bump. The more terms, the more bumps you can get.

Some of you may be wondering why this area of research is known as Algebraic Geometry – the algebra is clearly there, in the form of equations – but where’s the geometry?

Well, there are two problems here. Firstly, the type of algebra referred to in the name isn’t the kind of algebra you’ll remember from school, where you do the same thing to both sides of an equation and move terms around to get the answer. At university and research level, algebra is the branch of pure maths concerned with structures like groups and fields. Such objects are abstractly defined, and are essentially sets with rules. The set of all real numbers forms a field, because it’s a collection of things (numbers) you can combine together using addition and multiplication, and if you do this you always get another thing that lives in the same field (a number). There are a few other conditions to specify the different types of objects – called groups, rings, fields, and even algebras, and these can be used to describe real objects or structures – the group associated with moves on the Rubik’s cube being a nice example.

So algebraic geometry involves considering not just individual polynomials, but the ring of all possible polynomials, given the variables you’re putting in (sometimes just $x$, or sometimes a whole set of variables, usually labelled something like $x_1, x_2\ldots x_n$) and the field you’re using to pick coefficients (such as the real numbers, the set of all fractions, or the complex numbers).

The geometry aspect is slightly less obvious – but it has actually already started making itself apparent. By defining the linear polynomial* $y = 2x + 3$*, we’ve already seen how this corresponds to an object on a 2D graph. If your polynomial has more than one variable, this shape will exist in more than 2 dimensions. Each polynomial defines an object in space – a line, a plane or a solid, or anything else, and by studying the polynomials you can examine the geometry of these shapes and the connections between the abstract numerical object and the slightly more tangible (at least in lower dimensions) shapes. Algebraic curves (shapes defined by polynomials) range from simple lines and circles to beautiful complicated shapes with exciting names like the cycloid, the quadrifolium and the Conchoid of Nicomedes.

Birkar’s work in algebraic geometry concerns the structures you can construct from the rings of polynomials, how these generalise to higher dimensions, and how to deal with singularities in the space (points where the polynomial doesn’t look like a simple curve). His Fields medal was awarded for work on morphisms, maps used to ‘patch’ varieties (collections of polynomials) at points where they have singularities, so that they can be studied more easily.

Algebraic geometry connects to the study of shapes in topology, the use of polynomials to model mathematical problems, and it has connections to cryptography through the polynomials used in encryption, and to higher level physics concepts such as string theory. Since you’ve certainly already done a very small amount yourself – whenever you’ve sketched a graph of $x^2$ – you can maybe appreciate the importance of Birkar’s achievement and the beauty of this kind of mathematics, even if you’re not quite at Fields medal level yet.

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