AUTHOR'S PREFACE

On the afternoon of Monday, June 2, 1980, I was sitting at my desk when the phone rang. I recognized my brother’s voice immediately, but not its tone.

“Dad is at Presbyterian Hospital,” he said, his voice cracking. “He had a stroke.”

That evening, I walked into Dad’s hospital room and was shocked by his appearance. His face was lifeless. My brother Randy was there. “Mom was here but has gone home for the night,” he told me.

When the neurologist arrived, it was just the two of us. His report was unequivocal: Dad would never walk again or regain his speech. The stroke had destroyed a large portion of his left hemisphere, including Broca’s region—the center of speech production. We left in shock. Early the next morning, I sat with my mother in the bedroom and relayed the grim prognosis. 

What followed was a flurry of phone calls to friends and colleagues, breaking the news. I had always known Dad loved his work, but that night, I learned something new—his colleagues loved him, too. The pain in their voices revealed the depth of their admiration. It underscored an essential truth: the impact of his work was not just technical but deeply personal to those who had learned from him.

That moment of realization stayed with me 45 years till now, leading me back to the book I had begun in 2002 but set aside. Returning to the boxes stacked floor-to-ceiling in my closet, I was reminded that lack of material was never an issue—especially for the most transformative decade of his life: 1944–1954. 

In 1944, at 24 years old, he was just beginning to explore servomechanisms, married but childless, and earning 75 cents an hour at General Electric’s Schenectady Works. A decade later, he had authored two of the most cited papers in AIEE. Transactions, published a textbook with McGraw-Hill, moved into a custom-built home, had become a father of four, and a team leader at North American Aviation’s Aerophysics Laboratory, the nation’s preeminent developer of inertial guidance systems. His reputation was well established. His Spirule Company had already distributed its first 1,000 units—on its way to more than 100,000 units reaching universities in all 50 states and 65 countries.

Clearly, Dad’s transformative decade contained a story worth telling—but what was the story? I realized that it wasn’t just about the events or achievements. It was about the process, the evolution of ideas, and the interplay of influences that shaped his thinking. This book aims to weave together history, personal experience, and engineering breakthroughs to bring that journey to life.

The invention of the root locus method emerged from a confluence of factors: a lineage of analytical thinking passed down through family, the influence of inspirational teachers, a life partner who provided unwavering support, a habit of testing concepts through extreme cases, and the entrepreneurial environment at North American Aviation. Each of these was a "root" of root locus, shaping the way my father approached engineering. His method arose from a mindset that sought clarity, intuition, and practical verification.

No innovation stands alone. While Dad developed the method, others played crucial roles in refining and popularizing it. How should it be taught to engineers unfamiliar with the concept? Dad had strong opinions on these questions, but as with any evolving idea, external influences—feedback—shaped the outcome in unexpected ways. Understanding this process within the pivotal decade of 1944–1954 became central to this book.

Two years—1954 and 1980—were pivotal in Evans’ life. My memories of Dad go back to about 1954 when I turned seven. Looking back I realize I had two remarkable role models in one body: Dad—before and after his 1980 stroke.

Much of the credit for stabilityof our family is due to Mom, who wore many hats, all in a 118-pound package. Professor Robert Cannon called her "Saint Arline." The speech I gave in 1987 when Dad received the Rufus Oldenburger Medal was titled Life in the Left-Half Plane. That’s where stability lies. These themes—roots, feedback, and stability—form the foundation of this volume.

The neurologist’s predictions were not far off the mark, but thanks to my mother’s devotion, Dad lived a rewarding 19 years after his stroke, even teaching himself to draw with his left hand. Through this book, I hope to illuminate my father’s remarkable journey, resilience, and creativity—and to shed new light on how his contributions to engineering and art were shaped by the roots of root locus, the feedback that influenced its adoption, and the stability that my parents, working as a team, provided for me and my siblings.

Yes, there was a story to be told. And this is it. Greg Evans March 25, 2025