The simulation page lets you run best estimat (deterministic), probabilistic (Monte Carlo) or simulation table simulations (sequence). The error section lists problems that must be solved before a simulation can be made.
|Run||Starts a simulation.|
|Simulation settings…||Displays the simulation settings window. See simulation settings|
|Probabilistic settings…||Displays the settings window for probabilistic simulations. See probabilistic settings|
|Simulation table settings…||Displays the simulation table settings window. See simulation settings|
|Help||Displays this help page.|
This section lets you enter the start and end time as well as the type of simulation to perform.
The simulation section will display simulation progress as well as errors that need to be resolved before a simulation can be performed. The button will start a simulation, and the button will stop an ongoing simulation. The progress bar will show you how far the simulation has progressed. For deterministic simulations it will display the current time point, and for probabilistic simulations it will show the current iteration.
While the simulation is running, information about the simulation is presented here. If the simulation is aborted for some reason, the error causing the simulation to stop will be displayed here.
For a simulation to be run, the model need to be free of errors. The most typical error is a missing parameter value.
The simulation settings window contains four pages:
Here you specify the start and the end times for the simulation and output options.
|Note||For probabilistic, sensitivity analysis and simulation table simulations the output option should be Produce specified output only, otherwise only the start and end time is included in the result. A warning message will be presented in the error section. This is to limit the amount of data produced and to guarantee that the same time vector is returned from all simulations.|
In the case of the Linear time series the default value for the Min time is set to the Start Time and for the Max time is set to the End Time. In the case of the ‘Geometric’ time series the default values for the Min and the Max times is set to auto. * If you select ‘Linear Increment’ time series, enter the first and the last time in the Min and Max box respectively. Enter the increment in the increment box. The default value for the Min time is set to the Start Time and for the Max time is set to the End Time. For example: Start = 5, End = 10, Increment = 2.5 will return a time series with the values 5, 7.5 and 10.
The output page lets you choose simulation endpoints. All blocks of the project are displayed and are organized by sub-system. By selecting/unselecting either endpoints or whole sub-system nodes, you determine which simulation outputs will be available after the simulation is finished.
By removing simulation outputs the simulation time and memory consumption decreases. Also, the list of results will be shorter which makes it easier when creating charts and tables.
|Note||By default, values for all enabled blocks and parameters for all enabled contaminants will be returned from the simulation. To exclude contaminants from the simulation you must specify your contaminants in the context page.|
The solver page lets you select numerical solver and edit it’s settings. The solver to use depends on the model and the model parameters. For stiff problems you should start with the solver NDF, for non-stiff problems with DOPRI45.
Each solver has settings which control error tolerances and other specifics. Some common settings include:
Absolute tolerance - Absolute error tolerances that apply to the individual components of the solution vector. Absolute tolerance is a threshold value below which the value of the solution component is unimportant. The absolute error tolerances determine the accuracy when the solution approaches zero.
Default value = auto
Relative tolerance - Relative error tolerance that applies to all components of the solution vector y. This tolerance is a measure of the error relative to the size of each solution component. Roughly, it controls the number of correct digits in all solution components, except those smaller than thresholds defined in Absolute tolerance. The default, 1e-3, corresponds to 0.1% accuracy.
Default value = 0.0010
Limit data points to last - Maximum number of data-points to store. When the number of time points of a simulation exceeds this limit, the first values will be removed.
Default value = 1000
Before starting a probabilistic simulation there are certain settings to make. The minimum is to select which parameters to include in the probabilistic analysis.
Number of simulations - This setting specifies how many simulations will be performed during a probabilistic simulation. Default value = 1000
Seed - Initialises the seed value for the random number generator. If you set the same seed, then the sequence will be the same each run.
Sampling - Specifies the type of sampling used during the simulation, either Monte Carlo or Latin Hypercube sampling.
This page lets you select the parameters that will be included in the analysis. Only parameters that have been assigned probability density functions can be selected.
Note that you must select at least one parameter to run a probabilistic simulation.
Correlations between parameters can be assigned in order to reduce noise and to avoid impossible parameter combinations.
A probabilistic simulation starts with sampling values for all the probabilistic parameters, using either a (random) Monte Carlo scheme or Latin Hypercube sampling.
After the values are sorted so that correlated parameter values are used in the same iteration. For example, consider the parameters weight and height. These parameters are log-normally distributed and are positively correlated, meaning that it is common for heavy humans to also be tall. By assigning a correlation of say 0.5, the likelyhood of the weight parameter being large in the same iteration as the height parameter is large will increase.
To add correlations you must first select the Enabled button. You then click the Add button for each parameter pair, select the two parameters from the left and right lists and enter a correlation between the two.