xviii Preface to the second edition
previous discussions on blow-up of solutions, on group and phase velocities,
and on several further subjects. I have also updated and greatly increased
citations to books in the bibliography and have moved references to research
articles to within the text. There are countless further minor modiﬁcations
in notation and wording. Most importantly, I have added about 80 new
exercises, most quite interesting and some rather elaborate. There are now
over 200 in total.
And there is a yacht race among the problems for Chapter 10.
This second printing of the second edition corrects all known mistakes,
as of February, 2015.