HELP (Программа GPSS), страница 6

The Blocks Window has the best Debug Toolbar because you can select a Block Icon with the mouse, then click on the Place button to place a Stop Condition that HALTs the simulation when a Transaction attempts to enter that Block. When the Block is selected, if you click on the Remove button, the original Stop Condition is removed.

Most of the other Simulation Windows have toolbars without the Place and Remove buttons. But they do have the rest. Use the Halt button to send a HALT Command to the Simulation Object. The Continue button resumes the simulation and the Step button causes the simulation to attempt to enter a single Block, and then HALT.

You can view the collection of Stop Conditions in the User Stops Snapshot.

SELECT Window / Simulation Snapshots / User Stops

Figure 2—20. The User Stops Snapshot

The User Stops Snapshot displays the set of all active Stop Conditions. A Stop Condition is defined by a Transaction Number and a Block Entity Number. Any attempt of a Transaction of the stated number to enter a Block of the stated number causes a HALT Command to be invoked. The value of 0 is special. Since no Transaction or Block has a number of 0, this value is used to indicate "Any". For example, the window above shows a single Stop Condition that occurs when any Transaction attempts to enter Block 3.

Stop Conditions are added to the list using the STOP Command or via a Debug Toolbar. You can remove any or all Stop Conditions by STOP ,,OFF Command, via a Debug Toolbar, or by selecting and clicking the Remove or Remove All buttons in the User Stops Snapshot.

PLUS Traces

Whenyou are developing Model Objects that include your own PLUS Procedures, you should consider temporarily turning on the PLUS Trace in Page 2 of the Settings Notebook. Use Edit / Settings in the Main Window in order to do this. Then, PLUS Procedure invocations will be recorded by trace messages written to the Simulation's Journal Window.

You may find it useful to define a PLUS Procedure that takes one or more arguments but does nothing else. Then, you can insert invocations in your PLUS code that will cause traces of your User Variables to appear in the Journal Window. These can be easily removed after your PLUS Procedures are fully tested.

Experimentation

After you have established credibility in your GPSS Model, you typically enter the experimental phase of the project. During this period, you run your model repeatedly to experiment with the effects of proposed actions on your simulated system. It is up to you to establish that the effects you have observed in your simulations are above the statistical noise level. The Analysis of Varianceprovided by the ANOVAlibrary procedure can give you confidence that your results are due to more than just random variability.

The power of PLUS Experiments enables you to run complex experiments unattended, even exploring experimental response surfaces and collecting data for advanced statistical treatment. The Automatic Experiment Generators of GPSS World are at your disposal. Be sure to read Chapter 13 in this manual and study Lessons 19 and 20 in The GPSS World Tutorial Manual to get started with your experimentation.

Batch Mode

There is a background Batch Mode of operation that is useful when a large amount of processing is needed which does not require interactions on your part. Let's assume that the GPSS World Module Directory is either the DOS current directory or is listed in the PATH variable. From a DOS Command Line type

GPSSW FileSpec BATCH

where FileSpec is the file name of a Model Object or a Simulation Object. If the Objects are located in directories other than the GPSS World Module Directory, you should give a fully qualified pathname.

In Batch Mode GPSS World opens the object, and attempts to continue processing in a minimized window. If the Object is a Model, GPSS World automatically issues a Create Simulation menu command to translate it. If the Object is a Simulation, GPSS World passes a CONTINUE Command to it. You should insert an EXIT 1 Command or an Exit(1) invocation to close the session and save all the files.

You should not use Batch Mode until your Model has been well tested. Any Syntax Errors or Error Stops will cause the Session to be stopped. You will then have to deal with them by opening the window and interacting with the Session.

2.3.3. Artificial Limits

Memory Request Limits

An arbitrarymemorylimitisused to protect your simulations from gross overstatements of memory requests. It is used to trigger an error condition when a memory request exceeds the limit. It applies to allocations of Table Entities, Matrix Entities, and Plot Windows.

You can change the limit if you need to by altering the limit in the Simulate page of the Model Settings Notebook. Select Edit / Settings and turn to the Simulate page. Enter the new limit in the Max Memory Request entry field, and CLICK on OK.

Stack Size

The simulationstack is used for nested procedure calls. It is preallocated, and can cause a failure if it is not large enough when your simulation invokes PLUS Procedures to a deep nesting level. You can change the limit if you need to by altering the limit in the Simulate page of the Model Settings Notebook. Select Edit / Settings and turn to the Simulate page. Enter the new limit in the Stack Size entry field, and CLICK on OK.

Circular References

An arbitrary limit is used to protect your simulations from circular references. If your simulation uses highly nested GPSS, or PLUS procedure calls, it is possible that you may need to increase this value. You can change it in the Simulate page of the Model Settings Notebook. Select Edit / Settings and turn to the Simulate page. Enter the new limit in the Max Evaluation Depth entry field, and CLICK on OK

.

Edit Menu Commands

The Edit menu offers the following commands:

Undo Reverse previous editing operation.

Cut Deletes data from the GPSS World Object and moves it to the clipboard.

Copy Copies data from the GPSS World Object to the clipboard.

Paste Pastes data from the clipboard into the GPSS World Object.

Insert Line Inserts a line into the Text View of a GPSS World Object.

Delete Line Deletes a line from the Text View of a GPSS World Object.

Font Opens the Font Selection Dialog.

Expression Window Opens a Dialog to Modify an Expressions Window.

Plot WindowCommand Opens a Dialog to Modify a Plots Window.

Insert Block Opens the Menu for individual Block Dialogs.

Insert Experiment Opens a Dialog to Insert a Screening Experiment or an Optimizing Experiment.

SettingsCommand Opens a Dialog to View and/or Modify the GPSS World Object's Settings.

Undo Command ( Edit Menu )

Use this command to reverse the last editing action, if possible.

Shortcuts

Keys: CTRL+Z or

ALT-BACKSPACE

Cut Command ( Edit Menu )

Use this command to remove the currently selected data from the Object and put it on the clipboard. This command is unavailable if there is no data currently selected.

Cutting data to the clipboard replaces the contents previously stored there.

Shortcuts

Toolbar:

Keys: CTRL+X

Copy Command ( Edit Menu )

Use this command to copy selected data onto the clipboard. This command is unavailable if there is no data currently selected.

Copying data to the clipboard replaces the contents previously stored there.

Shortcuts

Toolbar:

Keys: CTRL+C

Paste Command ( Edit Menu )

Use this command to insert a copy of the clipboard contents at the insertion point. This command is unavailable if the clipboard is empty.

Shortcuts

Toolbar:

Keys: CTRL+V

Insert Line Command ( Edit Menu )

Use this menu command to insert a blank line into your Text View.

Shortcut

Keys: CTRL+I

Delete Line Command ( Edit Menu )

Use this menu command to delete the current line from your Text View. The current line is indicated by the position of the Insertion Bar.

Shortcut

Keys: CTRL+D

Font Menu Command ( Edit Menu )

Use Edit / Font to open a font selection dialog box. You can assign fonts and type sizes to all or part of the t

Edit Expressions Command ( Edit Menu )

Use this menu command to open the Edit Expressions Dialog. Doing so allows you to modify the contents of an Expressions Window.

Edit Plots Command ( Edit Menu )

Use this menu command to open the Edit Plots Dialog. Doing so allows you to modify the contents of a Plots Window.

Insert Experiment Command ( Edit Menu )

Use this menu command to open one of the Automatic Experiment Generator Dialogs. You can create either a Screening Experiment or an Optimizing Experiment.

Chapter 13 - Experimentation

This chapter tells you all about the experimentation features in GPSS World, and how to use them. A general overview is presented in the chapter introduction, followed by background material, then a detailed presentation of all the features relating to experimentation. We conclude the chapter with a list of practical tips that address problems you may encounter.

You should be able to get started after reading the introduction if you are willing to use the Help facilities, the Tutorial Manual, and refer to details in this manual. If you are unfamiliar with some of the nomenclature you may want to read section 13.2.2 first.

However, to get to most out of what GPSS World offers you need to become familiar with what lies in the rest of this chapter. Also helpful are several new sample models including OneWay.gps, Multiway.gps, ExperEther.gps, LatinSquare.gps, GraecoLatin.gps and Lessons 19 and 20 in the Tutorial Manual.

13.1 Introduction

The experimental phase of a simulation project assumes the existence of a fully developed, well-tested, GPSS World simulation that embodies the influences of each of the factors whose effects are to be measured. Only then, should you proceed with the experimental phase of your project. Conceptually, GPSS World supports three different approaches to experimentation: Screening Experiments, User Experiments, and Optimizing Experiments. There are features that support each of these.

The Experiments generated by GPSS World use partial factorial experiments with a fixed number of treatment levels for each factor. When you create your own experiments, you do not have this restriction. You are limited to 6 factors, each of which may have any number of treatment levels. Your job then is to define a one-way or an orthogonal experiment, fill a Result Matrix with the yield of each run, and pass it to the ANOVA library procedure.

13.1.1 Screening Experiments

A Screening Experiment is usually used to identify the most important factors affecting the simulated system. This information is crucial for directing the rest of the investigation in the most efficient way. The results of a screening experiment show which factors are not effective and should receive low priority with respect to further study. Also, the sensitivity of the yields of an experiment to one or more of the screened factors raises a flag that assumptions made in this part of the simulation should be verified carefully. GPSS World has an automatic experiment generator that can create Screening Experiments for you. To use it, you fill in a dialog that is accessed from the Edit Menu of the Main Window. This results in PLUS code being inserted into your Model Object. Optionally, this process will also load a Function Key with the appropriate CONDUCT Command for the simulation. After that, your role is to create the Simulation Object (Ctrl+Alt+S), start the experiment (normally F11), and then analyze the results.

13.1.2 User Experiments

User Experiments are more flexible, but you must create and run them yourself. Even so, GPSS World provides a lot of support along the way. The ultimate goal is for you to provide the data needed by the GPSS World ANOVA library procedure, which will analyze your experiments with up to 6 factors, including 2 and 3-way interactions between factors. The main requirement of GPSS World ANOVA is that you must pass it the name of the GPSS Matrix where the results of your experiment have been saved.

There are two important things to know about Result Matrices. First, before you begin your experiment you should initialize your Matrix's elements to the UNSPECIFIED state. Here's a typical Statement to do this:

INITIAL MyResultMatrix,UNSPECIFIED

This makes it clear to the ANOVA routine when a run of the experiment has not been completed.

The second thing is that if your experiment has more than one factor, you need to make it symmetrical so that the GPSS World ANOVA routine can cleanly analyze the variance. The technical term for this special symmetry is "orthogonality". All you have to do to achieve orthogonality is to look at all pairs of factors in your experiment. If, within each pair, each Treatment Level of the first Factor appears the same number of times within each Treatment Level of the second Factor, the experiment will be orthogonal. If you make everything symmetrical, it will be orthogonal. Don't worry, GPSS World will tell you when it's not.

GPSS World provides the PLUS Language that you can use to write programmable experiments. A good way to get started is to look at chapters 19 and 20 in the Tutorial Manual, or to use the automatic experiment generators in the Edit Menu to create samples for you to follow. Actually, you don't really need to use PLUS. You can set up your own Command lists in Include-files or enter them manually. All you need is some way to get the yield(s) of each run in your experiment into one or more Result Matrices that can be passed to the ANOVA library procedure.

If you do decide to write your experiment in PLUS, you should consider using the same programming style as the automatic experiment generators, which is discussed later in this chapter. The use of a Run Procedure is a case in point. A Run Procedure is a simple PLUS Procedure that is called every time a run in the experiment is to be performed. Since the Run Procedure is called by a PLUS Experiment, it is permitted to invoke the DoCommand library procedure, giving it the power to issue RMULT, START, RESET, and other Commands. It is then convenient to place all the Commands needed to set up each run into the Run Procedure. To reset variables in the Run Procedure, you should use the CLEAR ,OFF form of the CLEAR Command so that your Result Matrix is preserved. To vary the Random Number seeds, generated experiments pass a unique run number as an argument to the Run Procedure. However, you may prefer to do this in some other way. One last hint: since the command string passed to the DoCommand library procedure is eventually Translated in global scope, you must avoid using local argument and temporary variable names in it. If you need to use values from arguments or temporary variables, just build the command string dynamically before invoking DoCommand, as is done in the generated experiments. This is discussed further, below, in Section 13.3.2.

13.1.3 Optimizing Experiments

Optimization and the quantitative prediction of the behavior of a system are often the primary objectives of a simulation project. Both of these are supported directly by GPSS World. A Response Surface is an equation that predicts the results of a simulation. It is often desirable to establish a Response Surface for abbreviating results, providing a predictive methodology, quantifying the sensitivity of results to numerical inputs and other assumptions, and determining optimal treatment levels. GPSS World’s programmable Experiment feature provides the basis for a variety of Response Surface methodologies. A PLUS Experiment that calculates a Response Surface can be generated automatically, based on the input from a User Dialog. The resulting Experiment attempts to use the Method of Steepest Ascent and a Method of Local Exploration to find an optimum value. If successful, it reports the mathematical description of the best fit Response Surface and the predicted optimum conditions in the Journal Window of the Simulation Object.

As with Screening Experiments, the automatic generation of an Optimizing Experiment begins in the Edit Menu of the Main Window of GPSS World. When a Model Object is selected, you can click on Edit / Insert Experiment / Optimizing ... in order to open the dialog. After you fill in the blanks, and edit the Run Procedure, GPSS World inserts the finished PLUS Experiment into your model and optionally loads the appropriate CONDUCT Command into the F12 Function Key. Then, all you must do to start the experiment is to Create the Simulation Object (Ctrl+Alt+S) and press F12.