Preface xiii I would like to thank my wonderful teachers, even though many are no longer alive to receive this thanks. Olga Taussky Todd lured me into matrix theory with her course at Caltech and graciously accepted me as her doctoral student. In addition to my direct debt to her, she told me to take Herbert Ryser’s matrix theory course. Since I had already taken Ryser’s combinatorics course, this meant I had the good fortune to experience two years of mathematics presented with the utmost elegance, clarity, and precision. Much of the material for the chapters on zero-one matrices, Hadamard matrices, and designs comes from my notes from these courses and from Ryser’s book [Rys63]. After Caltech, I spent a year at the University of Wisconsin, where Hans Schneider kindly mentored me and gave me the chance to coteach a graduate matrix theory course with him. From Hans Schneider I learned of the Weyr characteristic, the connection between directed graphs and the Perron–Frobenius Theorem, and acquired the Wielandt notes [Wiel67]. I want to thank Charles Johnson, who hosted me for a semester of leave at the University of Maryland in 1984. Many thanks to Roger Horn, for inviting me to write the survey article [Sha91] on unitary similarity—this was how I came to relearn the Weyr normal form and to appreciate the power of Sylvester’s theorem. I also thank him for inviting me to write the American Mathematical Monthly article [Sha99] on the Weyr normal form and his patient corrections of my many errors misusing “which” and “that”. Alas, I fear I still have not mastered this. Going back further to undergraduate years at Kenyon College, thank you to all of my college mathematics teachers. Daniel Finkbeiner introduced me to the beautiful world of abstract mathematics in a first linear algebra course, followed by a second linear algebra course and more. Thanks to Robert Fesq for his Moore method abstract algebra course—I came to this course thinking seriously of being a math major, but this was the experience that sealed the deal. Thanks to Stephen Slack, both for a wonderful freshman course and then a Moore method course in topology. And thanks to Robert McLeod, both for his courses, and for generously giving his time to supervise me in an independent reading course my second year. And thanks also to Wendell Lindstrom for his beautiful course in abstract algebra. Finally, I was fortunate to have excellent math teachers in the Philadelphia public schools I mention here Mr. Kramer (sorry I don’t know his first name) of Northeast High School, for his tenth grade math class and twelfth grade calculus class.
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