Decide on "proportional band" versus "linearity region"

[Richard Murray]

In Ch 1 (introduction) and Ch 11 (pid) we use the term “proportional band” to refer to the range of inputs over which a proportional controller is linear. In Ch 2 (principles) we use the term “linearity range” to describe the same concept. In the first edition of the book we used the term “proportional band” in Ch 1, but it did not appear elsewhere.

Do we want to consolidate these terms? Which should we use?

[Richard Murray]

Using "linear region" to refer to the region in which the controller is operating linearly. Use "proportional band" as defined in industry: 100%/kp, with a short description. Updated in commit c048d84 and commit 9cee571.