Reference letter (Control Theories) Dear Sir or Madam: I gladly recommend my student Mr. Yi to you for his application to your graduate school program. Mr. Yi enrolled in my courses of "Digital Control System" and "Optimization Theory" during his senior year. In the former, he got a good score of 86/100 and ranked within top 5% of the class. In the latter which was opened for graduate students, he was one of the only three undergraduates who took this course. Throught the period of instruction, I found him an inquistive and attentive person. He always concentrated on my lectures and absorb knowledge profoundly. Although some of the assignments were somewhat difficult to the average students, he could solved them completely and correctly owing to his logical and analytical thinking and the clear conception to the theory. He also impressed me in the final project - developing a program to resolve the free-variable optimal problem. He thought deeply and did it skillfully, so the program could work very well even for the special cases (like cycling...) but still economically and easy to read. So I gave him the good score and was better than many graduate students. Besides, He also took a cluster of courses in Control and Systems Theory in his junior and senior years and always got good scores. Upon my observation, Mr. Yi has been fully prepared to undertake a Master in your institute in the control and system fields. I am confident that with the ingenious learning ability and diligent attitude that he has shown in the courses, he will be able to perform outstandingly even in a highly vigorous program. I have no hesitation in recommending him and hope that you will consider his application favorably.