David was nicknamed "fellow", as we all used to call him in college. That nickname was actually given to him by the Civil Engineering class that entered TaiDa one year before us -- for his being tall and hence they started calling him "fellow" for Longfellow, and we just carried on. David's freshman year was interrupted by a Pneumonia that sidelined him so long that he had to withdraw and then resumed his college career with our class. At the beginning of our second semester of our freshman year, around the spring of 1953, we promptly noticed him as a new comer to our class -- a tall and handsome guy quietly sat in the back of the classroom. I walked over to chat with him and we had become friend from that moment on. Through David, I got to meet his roommate Michael Hsu who later also transferred to our Civil Engineering Department from Mathematics. David, Michael, and I are all Catholic converts and that mutual faith has kept us close in college and ever since. We were active at Father Michael Chu's Sodality group during the years between our graduation and our successive coming to U. S. to pursue graduate studies.
The time period of 1963-1965 was a particularly memorable one for us and for me personally as David, Michael, and I were reunited in New York City. Michael was the first who had been working in New York City, David then came to Courant Institute of NYU to pursue the Ph.D. degree. And after an unsuccessful doctorate stunt at Cornell, I also found my way to New York City and jump-started my working career. We got together often just like when we were in Taipei. Time was also ripened as first Michael and then David to get married successively in 1964. My own wedding was scheduled in January, 1965. Those were the days of prohibitive international travel cost and excessive regulation paper works, few can generally expect or afford to bring family members over from Taiwan for weddings. So at my wedding, Michael represented my parents and David was the one that walked the bride down the aisle and handed her hands to me. One other of our CE56 classmates, James Ko, was kindly agreed to travel to NYC all the way from North Carolina on his own to be my Best Man. That was the time period we all, one by one, left our bachelorhood behind and embarked on the next phase of life.
Shortly afterward we slowly scattered away from New York City. I got a job to come to Detroit to join U.S. Army Corps of Engineers to do research on wind waves in the Great Lakes. Then David also came to Michigan upon receiving his Courant Institute Ph.D. to become a faculty member at Michigan State University, his Alma Mater of M.S. degree. Michael later also completed his Ph.D. study at City College of N.Y. and moved to West Coast. The following years we were all preoccupied at building careers and raising families. David and I are both in Michigan, but with 70 miles apart between Detroit and East Lansing, we didn't see each other much especially after children arrived. We got together a few times only when Father Chu came to visit us. I remembered once Father Chu celebrated a Mass in David’s living room. Michael once came to Detroit for business. When I resumed part-time doctoral study at University of Michigan, David once came down to Ann Arbor to attend a seminar given by a Cal Tech professor and we were able to have a brief reunion that day and spent some time together at the popular local hangout, the Browns Jug restaurant, on Michigan's central campus. My vivid memory also goes back to a dozen years before that day when I was still at Cornell, David and one of his Michigan Sate friends once drove all the way to Ithaca to visit me. That was the first time we got together in U.S. since we both left Taiwan. I accommodated him in the tiny living room of the small apartment I shared with some one, on a small sofa with two chair as extensions that can only support a part of his long body frame. But no worries, we sat there talked and talked all night, the two of us, hardly bothered to have any sleep at all.
David had a long and distinguished academic career at Michigan State. I was a little disappointed to notice that Michigan State did not preserve his web page for him as a Professor Emeritus. But I found out that many of his prominent publications can be readily downloaded from the Internet through Google search (with "David H.Y. Yen"), including at least two papers that David co-authored with our classmate Sing C. Tang. Sing was the one that first broke the news of David's passing to us. According to the Mathematics Genealogy Project of the American Mathematical Society, David had directed 11 Ph.D. students. That's a remarkable as well as admirable record. Somehow the Mathematic Genealogy Project did not seem to know that David was a doctoral student of Joseph B. Keller at NYU Courant Institute. Joe Keller, who later moved to Stanford, was one of the original members when Richard Courant first established the Applied Mathematics Institute that later bears his name.
I have no doubt that David is a great professor welcomed by students. I know that because I was just about the first informal college student he taught! Back to the second semester of our freshman year, while preparing for our sophomore year many had started getting a slide rule and so did I -- even though I did not even know how to use it at the time. David casually used a simple explanation that immediately opened my mind and became a slide rule user. When I first went to New York City, I know nothing about baseball. That was still the later stage of New York Yankee’s baseball domination. David patiently taught me all about baseball – so that I can go watching the baseball games with him on his television set in his apartment on the weekends. As he went to school in Michigan and became a Detroit Tigers fan there. Michael studied in Minnesota and naturally a Twins fan. Being in New York I was duly became a Yankee fan. To this day, now it’s 2011 World Series time again, every time when I watched a baseball game on TV, hearing those baseball jargons, I can still hearing David's voice in my mind patiently explaining those baseball terms to me.
In addition to be an accomplished professor of mathematics and mechanics, I am not sure that everyone knew that David is also a poet at heart. Back in the early 1950's, when we were still in our late adolescent stage, we both had tried our hands at writing poetry in modern Chinese and send to newspapers. I tried a few times, never succeeded, all were returned by the editor. But David did have at least one got accepted and gloriously published in the literary page of the Central Daily News. He used a pen name of 顏 曉. I am sure if one can go back looking through Central Daily News' archives of 1953, that poem should still be there. I don't remember the details now, but I do remember that was a beautiful poem that had my full admiration as I had never able to emulate. By the way, David picked the name "David" for himself after he read the whole massive novel "David Copperfield" by Charles Dickens in high school.
I remember there's a quote that says "True friend will leave footprints in your heart!" Indeed, David had definitely left a plenitude of footprints in my heart!
Finally if I may, I would like to show off this circa 1958 picture as how I'm remembering David from once upon a time when we were both young:
When we were beautifully young, they say that’s just an act of nature.
Then we turned old age, still beautifully, some think it’s a work of art.
Yes, it's all an art of God!
Saying farewell is hard as you have now departed.
Cherishing a lifelong friendship and thankful for the beautiful memories - -
Until we meet again, yes we most certainly will!
Over the life everlasting ever shall be!
I wish to express my wholehearted condolences to Lorraine, Alex, Earl, and Sarah. David is now in a much better place with no more physical suffering and reunited with his loving parents and old friends. I am certain he will get together with Father Chu and our CE56 classmate Father Richard Wang (Wang Ching-Hung) and they will jointly continue to pray for us here on earth.
David, rest in peace and pray for us!