[racket] A control-theory question

>> Start with a proportional controller (like Noel's suggestion), if it
>> doesn't *quite* get you to the set point and that steady state error
>> is an issue, add in the I and D terms.


Followup: that was very beautiful.  It works wonderfully.  Here's the patch:

    https://github.com/dyoo/mzscheme-vm/commit/6074fee7a77dbeae04a0bc9743ec7429713e2a43

I got to get rid of a lot of red code and replace it with a petite 12
lines of green code.  :)


Thanks again!