HEAT SINK
(Some energy is lost in
all interactions and from
all storage)


 -
 STATE VARIABLE
(storage) with inflows and
outflows


 SIMPLE ONE-WAY FLOW
BETWEEN TWO STATE VARIABLES


J2 = ky


 INTERACTION SYMBOL
(example' multiplier D or
divider )


 POSITIVE FEEDBACK
or autocatalytic growth
J = kxQ


 NEGATIVE FEEDBACK
or crowding effect, J =
kx(I-bQ)


CONSTANT GAIN AMPLIFIER
flow from E is proportional
to y.


SELF-MAINTAINING CONSUMER
MODULE (contains positive feed-
back for autocatalytic growth


PRODUCTION
 MODULE


 LOGIC FUNCTION:
COMPARATOR AND SWITCH
 J > 0 if x> c


SOURCE