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 at
     The module coded in Powersim Studio is at .
     A demonstration of half-life decay using this module can be found at F06HalfLifeDecay-SimulatorDemo.sip.

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