The calculus of friendship : what a teacher and a student learned about life while corresponding about math

181 Pages·4.445 MB·English

by  Joffray, Don, Joffray, Don / 1929- / Correspondence, Strogatz, Steven Henry, Strogatz, Steven H. / (Steven Henry) / Correspondence, Joffray, Don, Strogatz, Steven Henry

The Calculus of Friendship
e e e
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e
Calculus
The
Friendship
of
WhataTeacherand
a Student Learned
about Life
While Corresponding
about Math
Steven Strogatz
PRINCETONUNIVERSITYPRESS E PRINCETONANDOXFORD
Copyrightª2009byStevenStrogatz
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LibraryofCongressCataloging-in-PublicationData
Strogatz,StevenH.(StevenHenry)
Thecalculusoffriendship:whatateacherandastudentlearnedaboutlife
whilecorrespondingaboutmath=StevenStrogatz.
p.cm.
Includesbibliographicalreferencesandindex.
ISBN978-0-691-13493-2(hardback:alk.paper) 1. Strogatz,StevenH.
(StevenHenry)—Correspondence. 2. Joffray,Don,1929–
Correspondence. 3. Mathematicians—Correspondence.
4. Calculus. 5. Differentialequations. 6. Chaoticbehavior
insystems. I. Joffray,Don,1929– II. Title.
QA29.S698A42009
510.92’2—dc22 2008049339
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Dedicated to Mr. Joffray,
and to teachers like him everywhere
e e e
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Contents
Prologue ix
Continuity (1974–75) 1
Pursuit (1976) 8
Relativity (1977) 13
Irrationality (1978–79) 23
Shifts (1980–89) 34
Proof on a Place Mat (March 1989) 42
The Monk and the Mountain (1989–90) 71
Randomness (1990–91) 84
Infinity and Limits (1991) 94
Chaos (1992–95) 107
Celebration (1996–99) 115
The Path of Quickest Descent (2000–2003) 118
Bifurcation (2004) 128
Hero’s Formula (2005–Present) 140
Acknowledgments 155
Further Reading 157
Bibliography 161
Photography Credits 163
Index of Math Problems 165
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Prologue
For the past thirty years I’ve been corresponding with my
highschoolcalculusteacher,Mr.DonJoffray.Duringthat
time, he went from the prime of his career to retirement,
competed in whitewater kayak at the international level,
and lost a son. I matured from teenage math geek to Ivy
League professor, suffered the sudden death of a parent,
and blundered into a marriage destined to fail.
What’s remarkable is not that any of this took place—
suchupsanddownsaretobeexpectedinthreedecadesof
life—butratherthatsolittleofitisdiscussedintheletters.
Instead, our correspondence, and our friendship itself, is
based almost entirely on a shared love of calculus.
ItneveroccurredtomehowpeculiarthisisuntilCarole
(I’m happily remarried now) teased me about it. ‘‘You’ve
been writing to him for thirty years? You must know ev-
erythingabouteachother.’’Notreally,Isaid.Wejustwrite
aboutmathproblems.‘‘Thatissuchaguything,’’shesaid,
shaking her head.
Her question got me thinking. What did I really know
about my teacher? Why had so much gone undiscussed
between us? On the other hand, we both enjoyed our cor-
respondence the way it was, so was there any problem
here?
Questions like these have kept nagging at me. I’m not
sure how to go about answering them or if I should even
try.Allthewhile,Ifindmyselflookingforcluesinagreen