To get the same model behavior, compared to the end of the previous run, we have to copy the states of a model to the initial values.
When you use the Copy States command of the Simulation menu, 20-sim overwrites the initial values of the functions ddt, int, limint and resint with their current output states. This can be done at the end of a simulation run or at any point where a simulation run was interrupted.
You can reset the initial values to zero by using the Reset Initials command from the Simulation menu.
For some models, behavior at some operating point or "steady state" is of interest. Use the Copy States command to create simulation that directly starts at working level:
|1.||Run a simulation from t = 0 [s] until the operating point is reached. Use the Copy States command to store the states as new initial values. Now save the experiment using some special name.|
|2.||Now each time you open this experiment, simulations directly start at operating point.|
Consider the following first order linear model:
This model can be described by the dynamic equation:
output = int(0) + int( f(input,output) )
int(0) = the initial value of the integral
f(input,output) = input - K*output
In more general terms this equation can also be described as:
state = int(0) + int(rate)
rate = f(input, state)
When we start to simulate this model at t = 0 [s] the value of the integral is zero. The state is therefore equal to the initial value int(0):
state(0) = int(0)
At the end of a simulation, the integral may be unequal to zero. The state is therefore equal to:
state(end) = int(0) + int(rate(end)).
In other words, the value of the state is characteristic for the behavior of the model. To start a new simulation with the same behavior, we have to change the initial value to:
int(0) = state(end)
This is valid for all dynamic models: The states of a model are characteristic for its behavior. To get the same behavior, compared to the end of a previous run, we have to copy the states to the initial values.