A system of this type uses two energy sources, one renewable, the other nonrenewable. When the nonrenewable source is used up, the growth declines back to a steady state based on the renewable source.
Variables:N = nonrenewable energy source
J = steady inflow of energy
Q = stored biomass
K*JR*Q = part of J that goes into the system
K3 = increasing factor of Q
K7 = increasing factor of Q
K8 = decreasing factor of Q
Equations:DN = -K4*N*Q
JR = J/(1 + K*Q)
DQ = K7*N*Q + K3*JR*Q - K8*Q
Simulation:The graph shows the changes of N (red) and Q (green) over a time period.
Source code: Twosource.java
"What if" Experiments:
Think about the renewable and nonrenewable sources of our economy: