Work on Chapter 4 text.  Need to generate additional figure from expcircle.py, and add "reproduce fig 4.4" to the corresponding exercise.
Work on Chapter 4 text.  Need to generate additional figure from expcircle.py, and add "reproduce fig 4.4" to the corresponding exercise.

bueler/p4pdes,bueler/p4pdes,bueler/p4pdes,bueler/p4pdes