Problem 2 -- How to deal with "d" term.
The "d" term is an input to the system (in the same way that "r" is an input). Since this is a linear system you can examine inputs independently, so when computing Her you can set d = 0 and when computing Hyd you can set r = 0.
Also, there has been some confusion about the relationship between d and Fhill. Note that d = Fhill.
--Mary Dunlop 10:06, 6 November 2006 (PST)