This text predominantly targets the first year graduate students of mathematical science majors as well as the first and second year graduate students of engineering, physics, and operations research majors. A stronger senior undergraduate mathematics student can also benefit from the course. Some less theoretically oriented programs or those with weaker mathematics course curricula may find it reasonable to use the book for a three-semester course: with the first two semesters of basics and the third semester of advanced topics. The course can always be shortened to two semesters in such schools with the option to cover the first seven chapters, which are also quite sufficient for technical majors.