Steven Levingston is nonfiction editor of Book World and author of “Little Demon in the City of Light: A True Story of Murder and Mesmerism in Belle Époque Paris.”

The Mathematics of love
Patterns, Proofs, and the Search for the Ultimate Equation

By Hannah Fry

TED/Simon & Schuster.
113 pp. $16.99

Looking for a lover? Put down that comb, because it doesn’t matter how hot you are. “Actually,” Hannah Fry explains in “The Mathematics of Love,” “having some people think you are ugly can work in your favor.” For online dating, you can even stop fretting over your profile photo. Doing what most people do — hiding what makes you look unattractive — is exactly what you shouldn’t do. “When choosing a profile picture, you should play up to whatever makes you different — including the things that some people might not like,” Fry counsels. “So be proud of that bald patch, show off that ill-advised tattoo, and get that belly out.”

By her own admission, Fry has had a lamentable love life: “a mixed bag of successes mingled with a healthy series of disasters.” So why should we listen to anything she says about matters of the heart? Because, she asserts, she’s got mathematics on her side. Fry is a 30-something Brit, a mathematician and a complexity theorist who studies the connections between mathematics and human interaction at University College London. You can find her online giving TED talks in which she presents mathematical analysis of her favorite subjects: love and life’s complexity.

‘The Mathematics of Love: Patterns, Proofs, and the Search for the Ultimate Equation’ by Hannah Fry. (TED Books/ )

And now, just in time for Valentine’s Day, she has expanded one talk, “The Mathematics of Love,” into a smart, snappy guide to romance that dips into mathematical models — the golden ratio, regression analysis, the Gale-Shapley algorithm, discrete choice theory — to illustrate successful strategies for leveraging your looks, playing the online dating game, outdoing your friends in party pickups and deciding whether to have a fling. On-screen and on the page, Fry has a wry, chatty voice that illuminates age-old questions in brainy yet simple language. She summarizes tricky formulas but gladly admits that, when things get too gnarly for the general reader, she will provide only an abbreviated explanation of, say, optimal stopping theory, as this footnote reveals: “I’d like to explain it properly, but it really does get quite complicated. And let’s face it, we’ve all got lives to be getting on with.”

She dissects the patterns in the chaos of human relationships to create tips for sorting through the mysteries of love, attraction and beauty. She contends that long-held assumptions about beauty are based on some faulty math and science, which is good news for those who may not be gorgeous enough for the runway — that is, the majority of us. She takes issue with a long-established belief that human beauty is revealed in a mathematical concept called the “golden ratio,” a number about equal to 1.61803399, which relates to the optimal design characteristics of the face: “The perfect face should have a mouth that is 1.618 . . . times larger than the base of the nose, eyebrows that are 1.618 . . . times wider than the eyes, and so on.” What’s troubling about the golden ratio as a yardstick for beauty is the trickiness of the measurements required to establish such a hard-and-fast rule. “How do you decide where the ‘start’ of your ear is,” she writes, “or the point at which your nose definitively ‘ends’? And how do you do this to a degree of accuracy of five or more decimal places in your golden ratio measurement?”

Attraction, Fry gleefully reports, often sidesteps tidy mathematical equations because of the role of personal preferences. But knowing this, we can exploit mathematical formulas for luring the opposite sex or the same sex, as the case may be. “People who are unbelievably good looking,” she writes, “will always do well, of course.” But in the online dating world, you don’t necessarily have to be good-looking to be popular. Standing out — even for unattractive physical characteristics — can be just as important. Fry uses an analysis from the dating site OkCupid, co-founded by mathematician Christian Rudder, that draws on a technique known as regression analysis. OkCupid looked at the number of messages people received based on how others measured their attractiveness. Here’s the whopper: “Having people think you have a face like a dog’s dinner means you get more messages,” Fry says. People who were rated less attractive got more messages than people who were considered quite attractive but not amazingly beautiful. It seems counterintuitive, but, as Fry explains, “maybe what’s going on here is that the users sending the messages are also thinking about their own chances.”

If anyone still meets in the real world, Fry has the Gale-Shapley algorithm to help explain how partners find success in matching up. The algorithm suggests that people who make advances are much better at getting a desired partner than those who sit back and wait for someone to come to them. “If you put yourself out there, start at the top of the list [of your desired partners], and work your way down, you’ll always end up with the best possible person who’ll have you,” Fry writes. “If you can handle the cringe-inducing rejection, ultimately, taking the initiative will see you rewarded. . . . The math says so.”

You can help your cause by understanding that people make decisions based on options available to them, which in mathematical terms is known as discrete choice theory. The equations indicate that people follow fairly simple rules in making their decisions — and for ambitious suitors, it’s good to know that people’s choices can be easily manipulated. Fry draws on Dan Ariely’s work in behavioral economics to show the power, both in the consumer world and in dating, of a marketing ploy called the decoy effect. In marketing, the effect tricks us into buying a large popcorn at the movie theater after considering the varying prices of the small ($5) medium ($8) and large ($8.50). The medium, at just 50 cents less than the large, serves as a decoy to get us to spend extra for the large.

In dating, the decoy effect can be used to callous advantage while party-hopping by bringing along a buddy who is just slightly less attractive than you, so that you, like the minimally more expensive large popcorn, seem like the better option to potential shoppers.

Now suppose you’ve learned your math well and have a steady partner. But you still live in the real world among many temptations, including the lure of a fling. Beginning with a look at what’s known as the payoff matrix — the analysis of the pros and cons of a decision — Fry concludes that, though in some circumstances one party in the relationship may enjoy a greater payoff from an affair, the long-term effects on trust and cooperation are detrimental. “There’s little incentive to go for the short-term gain in cheating given how much you stand to lose in the long run,” she writes.

And so, Fry concludes, simple mathematical rules can be useful in life and love. “That’s why all mathematicians make famously excellent lovers (and dancers),” she quips. “Who knew math could give you such a lovely and moral way to live?”