Configuring the Sampling Technique and Execution Options

You use the General tab to select the sampling technique and to define the tuning parameters associated with the technique. In addition, you can define options that Isight uses when the component executes.

  1. Double-click the Monte Carlo component icon .
    The Monte Carlo Component Editor appears.
  2. From the Monte Carlo Component Editor, click the General tab.
  3. Choose one of the options from the Sampling Technique list.
    OptionDescription
    Descriptive Sampling This method is the recommended method. Fewer simulations are required to estimate the statistical characteristics of the system behavior.
    Simple Random Sampling This method is the default selection and is the most commonly used sampling method. Sample points for simulation are generated randomly and independently.
    Sobol Sampling This method generates numbers as binary fractions of appropriate length from a set of special binary fractions.

    The sampling technique’s options appear directly below the Sampling Technique list. Information about the technique appears in the Sampling Technique Description area on the right side of the editor.

    Sampling techniques in the Monte Carlo component are implemented as plug-ins. As such, they are extendable by creating new plug-ins for new sampling techniques. For more information, see Plug-In Development in the Isight Development Guide.

    For more detailed information on these sampling techniques, see About the Sampling Techniques.

  4. Set the following options in the Sampling Technique Options area:
    OptionDescription
    Number of Simulations Determine the number of simulations to be executed. The default number is 1000 for simple random sampling and 100 for descriptive sampling. A higher number of simulations specified generally results in an increase in the accuracy level of the statistical predictions.
    Use a fixed seed Select this option to manually specify the seed in the corresponding text box. If this option is not selected, Isight determines the seed randomly.
    Note: A fixed seed can also be set and used for the entire model. If a fixed seed is set for the model and also defined separately in the Monte Carlo component, Isight uses the one defined in the Monte Carlo component. If a fixed seed is set for the model and this option is not selected, the sequence of random numbers is based on the model’s random seed (and, thus, is still reproducible). For information about setting a fixed seed, see Setting the Execution Options in the Isight User’s Guide
  5. Set the following options in the Execution Options area:
    OptionDescription
    Execute Monte Carlo sample points in parallel Select this option if you want the sample points defined by the Monte Carlo simulation to execute in parallel. The convergence check interval may limit the number of sample points that are executed in parallel to batches that are the size specified for this convergence check interval.
    After execution, reset to mean value point and run With this option selected (default), after execution of all Monte Carlo simulation points, the random variables are set to their mean values and the Monte Carlo subflow executes one additional time. In this case, the Monte Carlo parameters (inputs and outputs) are left at the values calculated for this “mean value point.” If this option is not selected, the Monte Carlo parameters are left at the values associated with the last (random) Monte Carlo simulation point after execution.
    Convergence Check Interval This integer value specifies the frequency at which the convergence of the Monte Carlo response statistics (low order—mean and standard deviation) are checked. The default setting requires the convergence of response statistics to be checked after every 25 sample points. Decreasing this value may result in premature convergence; because the sample points are random, or in random order/combinations, sufficient sample points are needed to determine if the response statistics are estimated accurately. If this value is set to zero, then the convergence check is disabled.
    Convergence Tolerance This value is the Monte Carlo termination criterion, which specifies the fractional change in response mean and standard deviation that will allow the simulation to be terminated before reaching the specified number of simulations. For example, if you want the simulation process to stop if the change in the response statistics goes below 5%, enter a value of 0.05 in the corresponding text box. Convergence is checked after each set of simulations defined by the Convergence Check Interval (by default, after each set of 25 simulations). The default Convergence Tolerance is 0.001. If this value is set to zero, then the convergence check is disabled.
  6. If desired, click Advanced Options, and set the following options:
    OptionDescription
    Execute subflow only once If selected, the subflow executes only one time. This is useful in models that need to turn the driver logic on/off parametrically. This option is also helpful in the debugging process if the model does not execute successfully.

    Note: You can map this setting to a parameter. For more information, see Mapping Options and Attributes to Parameters.

    Allow the following items to be turned off by parameters Select this option if you want to turn off the selected types of design parameters (random variables, responses) using input parameters to the Monte Carlo components. If this option is selected, Boolean input parameters are created in an Active Random Variables/Active Responses aggregate under the Mapped Options and Attributes aggregate parameter. The parameters are selected by default. If any of the parameters are not selected at run time, those design parameters will not be used during execution.
    Import configuration at runtime Select this option if you want to import the Monte Carlo component configuration from a file at run time. If selected, Isight creates an input file parameter on the Monte Carlo component called Configuration. You can point the Configuration file to a specific file or map it from a file parameter from a previous component in the simulation process flow. Click the button to configure the file parameter to point to the desired file. You can also configure this file on the Design Gateway Files tab. For information about importing/exporting and the file format, see About Importing and Exporting Configuration Files.
  7. If desired, click the button to import all or part of the Monte Carlo component configuration from a file or to export the entire configuration to a file.

    This provides you with an easy mechanism for quickly configuring the component using information that comes from an external source without manually entering all the information in the component editor. For more information, see About Importing and Exporting Configuration Files.

  8. If desired, map an option to a parameter. For more information, see Mapping Options and Attributes to Parameters.
  9. Click OK to save your changes and to close the Monte Carlo Component Editor.