W. Magnus & S. Winkler 
Hill’s Equation [PDF ebook] 
Transformations, Approximation, Examples

Whilst the greatest effort has been made to ensure the quality of this text, due to the historical nature of this content, in some rare cases there may be minor issues with legibility. A particular problem. Also, we shall discuss some examples in detail, partly because they illustrate the general theory and partly because they appear frequently in applications. The section on the coexistence problem contains a little more than mere examples. It may be considered as a complete discussion of those results which can be.