Sensitivity Analysis Experiment

This experiment helps you to explore how sensitive are the simulation results to changes of the model parameters. The experiment runs the model multiple times varying one of the parameters and shows how the simulation output depends on it. For a single value type of output the chart "output vs parameter" is displayed. If the simulation output is a dataset (e.g. dynamics of a certain process in time), a series of curves is shown on one chart for comparison.

Creating a sensitivity analysis experiment

1. In the Projects view, right-click (Mac OS: Ctrl click) the model item and choose New > Experiment from the popup menu. The New Experiment dialog box is displayed.
   

2. Choose Sensitivity Analysis option in the Experiment Type list.
3. Type the experiment name in the Name edit box.
4. Choose the top-level agent of the experiment from the Top-level agent drop-down list.
5. If you want to apply model time settings from another experiment, leave the Copy model time settings from check box selected and choose the experiment in the drop-down list to the right.
6. Click Next to go to the next page of the wizard.
7. Here you choose the parameter you wish to vary and the way it is varied. The parameter you want to vary is selected in the Varied parameter drop-down list. Below this control you choose the way this parameter will be varied.
8. If you set your parameters to be Freeform varied, you should specify any stochastic expression evaluating the parameter value in the Expression field. It can be either a fixed value, or an expression evaluating the actual parameter value.In the Expression field of the use index to refer the iteration number (0,1,2,…).
9. Otherwise, if you set your parameters to be Varied in range, you should define Min, Max and Step values for the varied parameter.
10. Click Next to go to the Charts page of the wizard. Here you specify the charts that will display the simulation output. Each chart is defined in a separate row of the table: you should define Title, Type and Expression for each chart. Available types of charts are: dataset charts for datasets and scalar XY charts for scalar values of the varied parameter. You can use root in Expression.
11. Click Finish.

Properties

General

Name – The name of the experiment.

Since AnyLogic generates Java class for each experiment, please follow Java naming guidelines and start the name with an uppercase letter.

Ignore – If selected, the experiment is excluded from the model.

Top-level agent – Using the drop-down list, choose the top-level agent type for the experiment. The agent of this type will play a role of a root for the hierarchical tree of agents in your model.

Maximum available memory – The maximum size of Java heap allocated for the model.

Create default UI – The button creates the default UI for the experiment.

Please do not press this button since it will delete the experiment UI created by the wizard and will create the default UI for optimization experiment that may not correspond to your task.

Parameters

Varied in range – If selected, you should explicitly define the range of values for each parameter you want to vary. Namely, you define minimum and maximum values for a parameter and also the step this parameter will increase its value to reach the maximum.

Freeform – If selected, model is run for the fixed number of iterations you specify and the parameter values are calculated according to the expressions you define. Using the index keyword in the parameter value expression you can refer to the current model run number. Thus this mode also allows defining dependencies between the parameter value and other parameters and/or the number of the current model run.

Parameters – Here the user defines the set of varied parameters. The table lists all the parameters of the top level agent. To make a parameter a decision variable, click in the Type field and choose range there. If it is a numeric parameter, then specify the range for the parameter. Enter the parameter’s lower bound in the Min field, the parameter’s upper bound in the Max field, and specify the increment value in the Step field.

Model time

Stop – Defines, whether the model will Stop at specified time, Stop at specified date, or it will Never stop. In the first two cases, the stop time is specified using the Stop time/Stop date controls.

Start time – The initial time for the simulation time horizon.

Start date – The initial calendar date for the simulation time horizon.

Stop time – The final time for the simulation time horizon (the number of model time units for model to run before it will be stopped).

Stop date – The initial calendar date for the simulation time horizon.

Additional experiment stop conditions – Here you can define any number of additional experiment stop conditions. When any of these conditions will become true, experiment will be stopped. Condition can include checks of dataset mean confidence, variable values, etc. The top-level agent of the experiment can be accessed here as root, so if you want e.g. to stop the experiment when the variable plainVar of the experiment's top-level agent steps over the threshold, type here, say, root.plainVar>11. To make the condition active, select the checkbox in the corresponding row of the table.

Randomness

Random number generator – Here you specify, whether you want to initialize random number generator for this model randomly or with some fixed seed. This makes sense for stochastic models. Stochastic models require a random seed value for the pseudorandom number generator. In this case model runs cannot be reproduced since the model random number generator is initialized with different values for each model run. Specifying the fixed seed value, you initialize the model random number generator with the same value for each model run, thus the model runs are reproducible. Moreover, here you can substitute AnyLogic default RNG with your own RNG.

Random seed (unique simulation runs) – If selected, the seed value of the random number generator is random. In this case random number generator is initialized with the same value for each model run, and the model runs are unique (non-reproducible).

Fixed seed (reproducible simulation runs) – If selected, the seed value of the random number generator is fixed (specify it in the Seed value field). In this case random number generator is initialized with the same value for each model run, and the model runs are reproducible.

Custom generator (subclass of Random) – If for any reason you are not satisfied with the quality of the default random number generator Random, you can substitute it with your own one. Just prepare your custom RNG (it should be a subclass of the Java class Random, e.g. MyRandom), choose this particular option and type the expression returning an instance of your RNG in the field on the right, for example: new MyRandom() or new MyRandom( 1234 ) You can find more information here.

Replications

Use replications – if selected, the OptQuest Engine will run several replications per one simulation.

Fixed number of replications – if selected, fixed number of replications will be run per each simulation.

Replications per iteration – [enabled if Fixed number of replications is set] the fixed number of replications, which will be run per each simulation.

Varying number of replications (stop replications after minimum replications, when confidence level is reached) – if selected, varying number of replications will be run per each simulation. When running a varying number of replications, you will specify minimum and maximum number of replications to be run. The OptQuest Engine will always run the minimum number of replications for a solution. OptQuest then determines if more replications are needed. The OptQuest Engines stops evaluating a solution when one of the following occurs:

• The true objective value is within a given percentage of the mean of the replications to date.
• The current replication objective value is not converging.
• The maximum number of replications has been run.

Minimum replications – [enabled if Varying number of replications is set] – the minimum number of replications the OptQuest Engine will always run per one simulation.

Maximum replications – [enabled if Varying number of replications is set] – the maximum number of replications the OptQuest Engine can run per one simulation.

Confidence level – [enabled if Varying number of replications is set] – the confidence level to be evaluated for the objective.

Error percent – [enabled if Varying number of replications is set] – the percent of the objective for which the confidence level is determined.

Window

Window properties define the appearance of the model window, that will be shown, when the user starts the experiment. Note that the size of the experiment window is defined using the model frame and applies to all experiments and agent types of the model

Title – The title of the model window.

Enable zoom and panning – If selected, the user will be allowed to pan and zoom the model window.

Enable developer panel – Select/clear the checkbox to enable/disable the developer panel in the model window.

Show developer panel on start – [Enabled only if the Enable developer panel checkbox is selected] If selected, the developer panel will be shown by default in the model window every time you run the experiment.

Java actions

Initial experiment setup – The code executed on experiment setup.

Before each experiment run – The code executed before each simulation run.

Before simulation run – The code executed before simulation run. This code is run on setup of the model. At this moment the top-level agent of the model is already created, but the model is not started yet. You may perform here some actions with elements of the top-level agent, e.g assign actual parameter values here.

After simulation run – The code executed after simulation run. This code is executed when simulation engine finishes the model execution (Engine.finished() function is called). This code is not executed when you stop your model by clicking the Terminate execution button.

After iteration – The code executed after iteration run.

After experiment – The code executed after experiment run.

Advanced Java

Imports section – import statements needed for correct compilation of the experiment class' code. When Java code is generated, these statements are inserted before definition of the Java class.

Additional class code – Arbitrary member variables, nested classes, constants, and methods are defined here. This code will be inserted into the experiment class definition. You can access these class data members anywhere within this experiment.

Java machine arguments – Specify here Java machine arguments you want to apply on launching your model. You can find the detailed information on possible arguments at Java Sun Microsystems web site: http://java.sun.com/j2se/1.5.0/docs/tooldocs/windows/java.html

Command-line arguments – Here you can specify command line arguments you want to pass to your model. You can get the values of passed argument values in the experiment's Additional class code using the method String[] getCommandLineArguments()

Advanced

Allow parallel evaluations – If the option is selected and the processor has several cores, AnyLogic will run several experiment iterations in parallel on different processor cores. Thereby performance is multiply increased and the experiment is performed significantly quicker. This feature is made controllable because in some rare cases parallel evaluations may affect the optimizer strategy so that more iterations are required to find the optimal solution.
Do not use static variables, collections, table functions and custom distributions (check that their advanced option Static is deselected), if you turn on parallel evaluations here.

Load top-level agent from snapshot – If selected, the experiment will load the model state from the snapshot file specified in the control to the right. The experiment will be started from the time when the model state was saved.

Functions

You can use the following functions to control the experiment, retrieve the data on its execution status and use it as a framework for creating custom experiment UI.

Controlling execution

Function	Description
void run()	Starts the experiment execution from the current state. If the model does not exist yet, the function resets the experiment, creates and starts the model.
void pause()	Pauses the experiment execution.
void step()	Performs one step of experiment execution. If the model does not exist yet, the function resets the experiment, creates and starts the model.
void stop()	Terminates the experiment execution.
void close()	This function returns immediately and performs the following actions in a separate thread: Stops experiment if it is not stopped, Destroys the model, Closes the experiment window (only if the model is started in the application mode).
Experiment.State getState()	Returns the current state of the experiment: IDLE, PAUSED, RUNNING, FINISHED, ERROR, or PLEASE_WAIT.
double getRunTimeSeconds()	Returns the duration of the experiment execution in seconds, excluding pause times.
int getRunCount()	Returns the number of the current simulation run, i.e., the number of times the model was destroyed.
double getProgress()	Returns the progress of the experiment: a number between 0 and 1 corresponding to the currently completed part of the experiment (a proportion of completed iterations of the total number of iterations), or -1 if the progress cannot be calculated.
int getParallelEvaluatorsCount()	Returns the number of parallel evaluators used in this experiment. On multicore / multiprocessor systems that allow parallel execution this number may be greater than 1.

Iterations

Function	Description
int getCurrentIteration()	Returns the current value of iteration counter.
int getMaximumIterations()	Returns the total number of iterations.
int getNumberOfCompletedIterations()	Returns the number of completed iterations.

Replications

Before calling the Sensitivity Analysis experiment functions you may need to ensure that replications are used (call the isUseReplications() function).

Function	Description
boolean isUseReplications()	Returns true if the experiment uses replications; returns false otherwise.
int getCurrentReplication()	Returns the number of replications run so far for the current iteration.

Accessing the model

Function	Description
Engine getEngine()	Returns the engine executing the model. To access the model's top-level agent (typically, Main), call getEngine().getRoot();
IExperimentHost getExperimentHost()	Returns the experiment host object of the model, or some dummy object without functionality if the host object does not exist.

Restoring the model state from snapshot

Function	Description
void setLoadRootFromSnapshot( String snapshotFileName)	Tells the simulation experiment to load the top-level agent from AnyLogic snapshot file. This function is only available in AnyLogic Professional. Parameter: snapshotFileName - the name of the AnyLogic snapshot file, for example: "C:\\My Model.als"
boolean isLoadRootFromSnapshot()	Returns true if the experiment is configured to start the simulation from the state loaded from the snapshot file; returns false otherwise.
String getSnapshotFileName()	Returns the name of the snapshot file, from which this experiment is configured to start the simulation.

Error handling

Function	Description
RuntimeException error(Throwable cause, String errorText)	Signals an error during the model run by throwing a RuntimeException with errorText preceded by the agent full name. This function never returns, it throws runtime exception by itself. The return type is defined for the cases when you would like to use the following form of call: throw error("my message"); Parameters: cause - the cause (which will be saved for more detailed message), may be null. errorText - the text describing the error that will be displayed.
RuntimeException errorInModel(Throwable cause, String errorText)	Signals a model logic error during the model run by throwing a ModelException with specified error text preceded by the agent full name. This function never returns, it throws runtime exception by itself. The return type is defined for the cases when you would like to use the following form of call: throw errorInModel("my message"); This function differs from error() in the way of displaying error message: model logic errors are 'softer' than other errors, they use to happen in the models and signal the modeler that model might need some parameters adjustments. Examples are 'agent was unable to leave flowchart block because subsequent block was busy', 'insufficient capacity of pallet rack' etc. Parameters: cause - the cause (which will be saved for more detailed message), may be null. errorText - the text describing the error that will be displayed.
void onError (Throwable error)	This function may be overridden to perform custom handling of the errors that occurred during the model execution (i.e., errors in the action code of events, dynamic events, transitions, entry/exit codes of states, formulas, etc.). By default, this function does nothing as its definition is empty. To override it, you can add a function to the experiment, name it onError and define a single argument of the java.lang.Throwable for it. Parameter: error - an error which has occurred during event execution.
void onError (Throwable error, Agent root)	Similar to onError(Throwable error) function except that it provides one more argument to access the top-level (root) agent of the model. Parameters: error - an error which has occurred during event execution. root - the top-level (root) agent of the model. Useful for experiments with multiple runs executed in parallel. May be null in some cases (e.g. on errors during top-level agent creation).

Command-line arguments

Function	Description
String[] getCommandLineArguments()	Returns an array of command-line arguments passed to this experiment on model start. Never returns null: if no arguments are passed, an empty array is returned. You can call this function in the experiment's Additional class code.