System Dynamics Modules
First Order Linear Negative Feedback
The first-order negative feedback module comprises a stock progressively depleted
at a fractional decay rate. At any time, the absolute
value of the decay is indicted by the content of
the stock. More correctly, the initial sate will be depleted
over time to become the current state—the extent of the
decay can be gauged by counting all that flows out
over the period of interest. Rate of change of state
is negative and numerically equal to the product of the
current state of the system and a constant.
A first-order negative
feedback has the effect (each time we calculate it) of
subtracting from S an amount (where the constant is a
Fractional Decay Factor ‘d’) which is less than the previous
time we calculated it. Consider a series of calculations at
times t0, t1, t2 ... tn, with the initial
value of S being S0 and a Fractional Decay Factor
d operating on the outflow.
The description of the module is
The module coded in Powersim Studio is
A demonstration of half-life decay using this
module can be found at F06HalfLifeDecay-SimulatorDemo.sip.
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