This book was motivated by my teaching of the subject to graduate students at the Hong Kong University of Science and Technology (HKUST). My interest-rate class usually consists of students working toward both research degrees and professional degrees; their interests and levels of mathematical sophistication vary quite a bit. To meet the needs of the students with diverse backgrounds, I must choose materials that are interesting to the majority of them, and strike a balance between theory and application when delivering the course materials. These considerations, together with my own preferences, have shaped a coherent course curriculum that seems to work well. Given this success, I decided to write a book based on that curriculum.

这本书是由我在香港科技大学（香港科技大学）的研究生教授所教授的。我的兴趣班通常由攻读研究学位和专业学位的学生组成；他们的兴趣和数学复杂程度相差很大。为了满足不同背景的学生的需要，我必须选择大多数学生感兴趣的材料，并在提供课程材料时兼顾理论和应用。这些考虑，加上我自己的喜好，形成了一个连贯的课程，似乎效果不错。鉴于这一成功，我决定根据这门课程写一本书。