What is mathematics of physics and engineering? An immediate answer
would be "all mathematics that is used in physics and engineering", which is
pretty much ... all the mathematics there is. While it is nearly impossible
to present all mathematics in a single book, many books on the subject
seem to try this.
On the other hand, a semester-long course in mathematics of physics
and engineering is a more well-defined notion, and is present in most universities. Usually, this course is designed for advanced undergraduate students
who are majoring in physics or engineering, and who are already familiar
with multi-variable calculus and ordinary differential equations. The basic
topics in such a course include introduction to Fourier analysis and partial
differential equations, as well as a review of vector analysis and selected topics from complex analysis and ordinary differential equations. It is therefore
useful to have a book that covers these topics — and nothing else. Besides
the purely practical benefits, related to the reduction of the physical dimensions of the volume the students must carry around, the reduction of
the number of topics covered has other advantages over the existing lengthy
texts on engineering mathematics.