EZStrobe.com

Learning EZStrobe

2011-02-28T23:07:00.000-05:00

In the Stroboscope program group you will a PDF tutorial on EZStrobe which is meant to accompany the EZStrobe Introduction paper, which in turn is available at the Winter Simulation Conference archives. That short paper explains nearly all of of the concepts that make up EZStrobe and explains how to model an earthmoving operation that includes a long one-way segment. The tutorial shows how to build such a model incrementally.

The following articles provide useful EZStrobe modeling information as well:

EZStrobe Model Options.

EZStrobe ACD Animation.

Queues and Their Properties.

Multi-Step Activities in EZStrobe with Identical and Consecutive Steps.

Multi-Step Activities in EZStrobe with Non Identical or Non Consecutive Steps.

EZStrobe is based upon work supported by the National Science Foundation under Grant No. 9733267. Any opinions, findings, and conclusions or recommendations are those of the author(s) and do not necessarily reflect the views of the National Science Foundation.

EZStrobe ACD Animation

2011-02-28T20:40:00.001-05:00

The first model of a complex system is rarely a correct representation of the modelers’ understanding of the real system. By running the model and analyzing its output it is often possible to detect some errors, other errors may not be readily apparent and may go undetected.

EZStrobe offers graphical and interactive model verification (debugging) by means of model animation. EZStrobe’s animation capabilities are designed specifically for the model developer to understand and gain confidence in the model’s correctness. The animator graphically illustrates the dynamic state of the simulation (e.g., current content of queues and number of ongoing activity instances) and the events that take place during simulation (e.g., when an instance of an activity starts or ends, when a queue receives resources, or when resources flow through links).

Controlling the Animation

When running a simulation of an EZStrobe model that has the Animate and enable breakpoints option turned on in the Model Options form, EZStrobe presents the Simulation Controller shown below.

To start animation click the Begin button. The animation will proceed at a speed that depends on the position of the Animation Speed slider. The speed can be decreased or increased while the animation is going on. To pause the animation at the next event, check the Next event option. The simulation will pause immediately. The Simulation Controller during a pause looks like this:

The Begin button changes to a Continue, and the current simulation time is displayed below the progress bar.

While an animation is paused or after it has ended you can right-click any activity or Queue in the ACD to see the current values of most statistics associated with it. Right-clicking over a Queue, for example, will show a context menu similar to the one shown below.

Whereas right-clicking over an activity will show a context menu similar to the one shown below.

The displayed statistics are meant to always be up to date, but in some rare instances they may not be. If you suspect that the statistics shown when right-clicking a modeling element are not up to date, you can force an update by clicking the Update Node Statistics button.

Clicking the Continue button will resume animation. To watch an animation step by step, continue to click the Continue button without turning off the Next event option. To take steps that encompass all the events that take place at a given time, turn on the Clock advance option and turn off the Next event option.

To continue animating and stop only after the simulation reaches a specified time, uncheck the Clock advance and Next event options, type the time at which you want the simulation to stop in the provided input box, and turn on the Time option. This can be done whether the animation is ongoing or paused.

To make the simulation proceed without animation, and consequently at a much greater speed, you can turn off the Animate option. While the animation continues you can turn on the Clock Advance option to make it pause when the simulation clock advances, or set a time and turn on the Time option to stop it then. Once it is paused you can turn on the Animate option and continue or view step by step.

To finish the animation and the simulation you can click the End Model button at any time.

Do not change any aspect of the model such as editing the parameters of a Queue or activity while the simulation is running, since the changes will be ignored until the next time the simulation runs.

If you are not interested in watching the animation, turn off the model option to Animate and Enable breakpoints prior to running the simulation, rather than turning off the Animate option in the Simulation Controller. The simulation will run up to 10 times faster this way.

Understanding the Animation

The portion of an EZStrobe ACD below shows a paused animation that can be used to understand things by example.

The thick red border on DumpBucket indicates that one of its instances is terminating. Specifically, the 20 on the top right indicates the specific instance that is finishing (zero based count). The 1/21 in the top middle indicates that one instance is currently taking place (the one terminating) and that 21 have started since model execution began. The blue thick border on SwingEmpty indicates that one of its instances is starting (this happens while an instance of DumpBucket is terminating). The 20 on the top left of the activity indicates the specific instance that will start. The 0/20 in the top middle indicates that no instances are taking place (the one currently starting does not count until after its duration has been sampled), and that a total of 20 have begun. The thick line used for the link that connects DumpBucket to SlInTrk indicates that 2.5 resource units are being sent to the Queue. The 5 at the top of SlInTrk indicates its current content. If the Continue button is pressed on the controller, the link’s line will return to normal thickness, SlInTrk’s border will turn thick, and the number on top will be updated to 7.5.

Queues and Their Properties

2011-02-28T12:20:00.001-05:00

Queues are Activity Cycle Diagram (ACD) nodes that hold resources. Resources get there by initialization at the start of simulation, or when instances of activities that precede it finish and release resources. The resources in a Queue are removed from them when Combi activities start (create an instance of themselves) and draw resources from them.

The portion of an ACD below shows a Queue that is initialized with 16 resources. It has two links that lead into it: the Pred activity (could be a Normal or a Combi) which releases 3 resources to the Queue whenever instances of Pred finish; and some other activity from the bottom (not shown) that releases 1 resource whenever its instances finish. Links from Queues can only lead to the Combi activities that draw resources from it. In the ACD below, two Combi activities draw from Queue: the Succ Combi which draws 6 resources whenever it starts, and some other Combi at the right (not shown) which draws 1 resource.

In the ACD above, only the name of the Queue and its initial content are specified in the Queue Properties form. To bring up the the Queue Properties form double-click the Queue. The other information shown is defined by the links that release resources to, or that draw resources from, the Queue.

Queue Statistics

As a simulation proceeds, a Queue collects statistics that are calculated on the basis of a graph of Queue content as a function of simulation time like the one shown below:

The graph above goes from simulation time 0 to simulation time 1.9. Imagine that the graph is drawn by initially setting the pencil down at 0,0 and never lifting it up while drawing as indicated by the arrow heads.

The list below shows the Queue statistics, how they are calculated, and how they can be accessed in formulas (shown in parenthesis below the Queue statistic name). For the calculations it is necessary to know the area under the graph (15.1 res-time units) as well as the area under a graph of the content squared (126.3 res²-time units).

Current Content (Queue.CurCount)	The current content is the height of the graph at the pencil’s last position. In the graph above this is 10 res units.
Average Content (Queue.AveCount)	The average height of the graph. Obtained by dividing the area under the graph by the simulation time. In the graph above the average content is 15.1/1.9=7.95 res units.
Content Standard Deviation (Queue.SDCount)	The standard deviation of the height of the graph. Indicates the variability of the content. If M denotes the area under a graph of the content squared, the Standard Deviation is sqrt[(M/SimTime)-AveCount²]. In the graph above the standard deviation of the content is sqrt[(126.3/1.9)-7.95²]=1.82 res units.
Minimum Content (Queue.MinCount)	The height of the graph at its lowest point. Considering the part of the graph after the Queue has been initialized. In the graph above the minimum content is 4 res units.
Maximum Content (Queue.MaxCount)	The height of the graph at its highest point. In the graph above the maximum content is 16 res units.
Total Content (Queue.TotCount)	The total number of resource units that have entered the Queue. Obtained by adding the length of all the “up” movements of the pencil, shown in red in the graph above. The total content of the graph above is 34 res units.
Average Wait (Queue.AveWait)	The average time spent by resources in the Queue. This is obtained by dividing the area under the graph by the Queue’s Total Content. The average wait thus considers the time that resources currently in the Queue have been waiting, not just those that have already left. The average wait in the graph above is 15.1/34=0.44 time units.
Last Amount Received (Queue.LastAmtReceived)	The length of the last “up” movement of the pencil. The last amount received in the graph above is 1 res unit.

Additional Queue Options and Statistics

EZStrobe can collect more detailed statistics about Queues than those mentioned above. If Microsoft Excel is available, EZStrobe can also create a chart of Queue content as a function of time.

The Queue Properties form has two pages. To invoke it, double-click the Queue. The first page, Basic Properties, is shown below.

The Graph population vs time option tells EZStrobe to create a graph of Queue content as a function of time in Excel. This option significantly slows down simulations and the graphs it produces need to be customized in Excel to suit specific needs. However, when selected for Queues whose content over time is of interest, it is very useful. The Queue Statistics Graph shown earlier in this article was customized after EZStrobe initially created it. The graphs produced by EZStrobe include markers for each point and a thick line type, which make these graphs attractive only when they contain a handful of data points. Hiding point markers and reducing the portion of the graph that is visible by adjusting the x-axis properties are typically necessary to make these graphs attractive.

The Collect statistics in bins option tells EZStrobe to collect the data needed for a histogram of Queue content as a function of time. The number of bins specified in the Bins field are created between the From and To values. Underflow and overflow bins are also created. The bin output will appear in the simulation report in the Stroboscope IDE and, for 14 bins between 4 and 18, will look like this:

   Content     TotTime %Time
=============================
    < 4.00        0.00   0.00
    < 5.00        0.05   2.63
    < 6.00        0.15   7.89
    < 7.00        0.50 26.32
    < 8.00        0.85 44.74
    < 9.00        1.05 55.26
   < 10.00        1.40 73.68
   < 11.00        1.80 94.74
   < 12.00        1.90 100.00
   < 13.00        1.90 100.00
   < 14.00        1.90 100.00
   < 15.00        1.90 100.00
   < 16.00        1.90 100.00
   < 17.00        1.90 100.00
   < 18.00        1.90 100.00
>= 18.00        0.00   0.00

The output above indicates, for example, that the percentage of time that the Queue contained less than 7 resources was 26.32%, and that the total time that the Queue content was greater than or equal to 7 but less than 8 was 0.85-0.50=0.35 time units.

Integral Statistics

The second page of the Queue Properties form, Integral Statistics, is for the collection of statistics for the Queue on the basis of a larger unit than that modeled by the Queue. The Integral Statistics page for the model used in Multi-Step Activities in EZStrobe – Non Identical or Non Consecutive Steps is shown below. Please see that article for detailed explanation of Integral Statistics. In essence, rather than plotting Queue content as a function of time, Integral Statistics graph the integer part of the Queue content after it has been divided by a Divisor.

EZStrobe Model Options

2011-02-27T22:10:00.001-05:00

In EZStrobe, almost everything that defines a model is visible in the model’s activity cycle diagram. Exceptions are:

The simulation stopping conditions.
The number of random number streams and the seed used to initialize them.
Some options for extended collection of statistics associated with Queues.
The number of replications.
Whether to animate the activity cycle diagram during simulation.
Whether to generate a trace file in the Stroboscope output.

All the above, except those related to extended Queue statistics, are visible and editable in the Model Options form. To invoke this form, right-click on an unoccupied space of a model page and select Edit Model Parameters.

The Model Options form with its default values is shown below:

Simulation Stop Conditions

The options most relevant to the behavior of the model are those grouped under Simulation Stop Conditions.

The Time limit, as its name indicates, will stop a simulation as soon as the simulated time exceeds the specified value. The default is 100,000 time units. Many beginner simulations are designed to stop when no more resources are available to continue simulating, which usually indicates that the desired amount of work represented by the operation is completed. The default Time limit is set at 100,000 so that an incorrectly prepared model will stop at some point rather than keep on going forever. A common beginner mistake is to leave the Time limit at its default value in simulations that are expected to last much longer (in terms of simulated time) – in these cases the amount of work simulated will be smaller than that desired. For cases where a model is known to work correctly, it is advisable to set the Time limit to a very large number, such as 10^300 (which is close to 10^308, the largest possible time that simulation can reach without generating an overflow error).

If a Control activity is specified, simulation will stop as soon as the indicated activity starts the number of times specified in the Limit field to its right.

If a Control queue is specified, simulation will stop as soon as the content of the indicated queue reaches the value specified in the Limit field to its right.

Simulation will stop when any of the stopping conditions is reached. If the reason for termination is the inability to continue because no more activities can be instantiated with the current resources available, the simulation output will indicate that the Future Events List is empty at the time of simulation end.

Random Number Control

Stochastic simulations such as those modeled by EZStrobe depend on random numbers to incorporate uncertainty. When a Seed is specified in the Model Options, the sequence of random numbers used (and as a consequence the output) will be identical, regardless of how often the simulation is run. If a Seed is not used, every simulation will develop in different ways and yield different results. Although different, these results will follow a certain distribution which is the truly useful outcome. Setting a Seed is useful during model development because it allows the modeler to follow the steps of a simulation in an identical manner between runs.

More sophisticated models, especially those whose output need to be compared with those of another alternative model, need to use a separate and independent stream of random numbers for each source of uncertainty. The Number of Streams tells EZStrobe how many independent random number streams to make available to the simulation. When a Number of Streams is specified, functions that sample from probability distributions allow an extra parameter to specify the stream that will be used to generate samples. The number specified must be equal to or smaller than the Number of Streams specified in the Model Options.

Single Replication Options

When a model is being run only once, particularly during its development, the Single Replication Options enable EZStrobe’s model verifcation (debugging) features.

When Animate and enable breakpoints is checked, simulations will animate the model’s network and allow it to proceed automatically, by time step, or by event. More details are available in the article EZStrobe ACD Animation. When a model is not being verified, the Animate and enable breakpoints options should be turned off, since this will result in a simulation speed orders of magnitude faster.

When Produce a trace output for debugging is checked, a second output will be generated in the Stroboscope IDE when the simulation is run. This output will contain a sequential listing of all the events that occurred in a simulation. The details that are output can be controlled using Stroboscope’s trace options invoked using the menu sequence File->Options…->Trace Flags in the Stroboscope IDE. This option is available for advanced modelers. Most EZStrobe verification can be carried out more effectively using EZStrobe ACD animation.

Multiple Replications

When a model is fully verified and believed to be completely correct, it is useful to run the simulation multiple times in order to understand the distribution of selected model outputs. To do this, you can specify the Number of simulations to run. When more than one single replication is specified, EZStrobe will produce tabular output with one row for each simulation run. In each row, the values of all Results will be listed, with the exception of those that have their No Print Result property set to True.

Multi-Step Activities in EZStrobe – Identical Consecutive Steps

2011-02-26T23:03:00.001-05:00

Sometimes the modeler has the choice, or the data, to model an activity that consists of n multiple identical steps as one long activity or as a n consecutive shorter activities. An example is loading a flatbed truck with five pre-fabricated beams using a crane. The modeler can choose to represent the loading activity as one activity that represents loading all five beams, or as five consecutive activities each of which represents loading one beam.

The most effective way to model such cases is to use one single activity that captures all the steps. This is possible if:

The resources involved remain committed to the activity during all steps (e.g.. if a crane starts loading a flatbed only when five beams are available and it never stops to do something else until all five beams are loaded.
The distribution of the time required for the completion of all the steps required is available (e.g., the modeler knows the distribution of the time it takes to load five beams).

The EZStrobe network below (click it to see in detail) illustrates two such activities: One for loading five beams at the fabrication site and another for unloading them at the job site:

The time to load (LoadTm) or unload (UnloadTm) all five beams is defined using an EZStrobe Result that contains the appropriate distribution, for example ScaledBeta[5,10,8,8] (minutes). Note that EZStrobe Results must be used in order for each activity instance to sample a new duration to obtain its time. If EZStrobe Parameters are used instead, EZStrobe will sample once at the start of the simulation to establish the value of each parameter, which will retain that value from then on. As a consequence, all instances of each activity will have the same duration rather than be sampled from the distribution to establish the time of each instance.

The exact same network can be used when the distribution of the time required for the completion of all the steps required is not available, if:

The distribution of each step is known (e.g., the modeler knows the distribution of the time it takes to load one beam).
The number of multiple identical steps that make up a long activity is relatively small.

This can be achieved by setting the distribution of the time for the activity as the explicit sum of samples from the distribution of the time for each step. For example, if the modeler knows that the distribution of the time to load or unload one beam is Uniform[1,2] (minutes), the LoadTm and UnloadTm EZStrobe Results can be defined as Uniform[1,2]+Uniform[1,2]+Uniform[1,2]+Uniform[1,2]+Uniform[1,2]. If the number of steps is large then it becomes cumbersome to define the results appropriately, although EZStrobe will actually allow the formula for a result to be up to 64k characters in length.

Note that the sum of 5 independent samples from Uniform[1,2] is not the same as 5*Uniform[1,2], which multiplies one sample by 5 and is uniformly distributed between 5 and 10. The sum of 5 independent samples from a uniform distribution between 1 and 2 is actually an Irwin-Hall distribution with parameter 5 (quite close to a Beta distribution with both shape parameters set to 8), scaled and translated to the range [5,10].

Please see the article Multi-Step Activities in EZStrobe – Non Identical Consecutive Steps, to see how to model multi-step activities when the steps required are not Independent and Identically Distributed (IID), when the number of steps required is variable, or when the multi-step activity can be interrupted between steps.

The model for this article can be obtained here. It has a seed and uses multiple random number streams so that it yields the exact same output as other models that are supposed to be identical.

Multi-Step Activities in EZStrobe – Non Identical or Non Consecutive Steps

2011-02-26T15:49:00.000-05:00

Sometimes a modeler needs to represent an activity that consists of multiple steps as a series of shorter activities. An example is loading a flatbed with five pre-fabricated beams using a crane. This article describes how to model this situation when the time required for steps are not Independent and Identically Distributed (IID), when the number of steps required is variable, or when the multi-step activity can be interrupted between steps. The cases where none of these conditions exist can be modeled much more simply and efficiently as described in the article Multi-Step Activities in EZStrobe – Identical Consecutive Steps.

The best way to represent multi-step activities consisting of non identical continuous steps is to use an activity to model each step.

The EZStrobe network below (click it to see in detail) illustrates two such activities: One for loading one beam to a flatbed truck at the fabrication site and another for unloading it at the job site. Trucks do not explicitly circulate in the network, what circulates instead is the space required for (or occupied by) each beam in the truck. Five occupied spaces are needed for transportation to the jobsite. Five unoccupied spaces are needed for return to the fabrication site. The Load activity moves one unoccupied space waiting to load (in the BmSpotsWtLd queue) to an occupied space waiting to be transported (in the BmSpotsLdd queue) :

The time to load (LoadTm) or unload (UnloadTm) one beam is defined using an EZStrobe Result that contains the appropriate distribution, for example Uniform[1,2] (minutes). Note that EZStrobe Results must be used in order for each activity instance to sample a new duration to obtain its time. If EZStrobe Parameters are used instead, EZStrobe will sample once at the start of the simulation to establish the value of each parameter, which will retain that value from then on. As a consequence, all instances of each activity will have the same duration rather than be sampled from the distribution to establish the time of each instance.

The network above models the exact same operation as the network in the article for identical consecutive steps. Running both networks will give the same total simulation time, the same system production in transported beams per hour, and the same utilization for the cranes that load and unload.

Since this network does not explicitly represent trucks as single units, it is not capable of providing statistics related to the waiting time and utilization of trucks.

The difference in what is represented by the several queues containing trucks compared to beam space in trucks, is illustrated by a plot of their population as a function of time. The plot below is for the first 120 minutes for trucks waiting to load when they are modeled explicitly:

Whereas the plot below is for the exact same 120 minutes for the beam space waiting to be occupied, when the truck space is modeled instead:

The relationship between the two might be easier to appreciate in the combined chart below:

As can be seen above, 4 or less beam spots mean 0 trucks, 5 to 9 beam spots mean 1 truck, 10 to 14 trucks mean 2 trucks, and so on. The number of trucks can be calculated by taking the integer part of the number of spots divided by 5, e.g., Trucks==Int[Spots/5].

Queue Integral Stats

For queues, EZStrobe allows the definition of Integral Stats, which allow the collection of statistics in terms of a larger flow unit than the one modeled in the queue. Integral Stats require a name and the number of modeled units that make up the larger unit (called the Divisor).

In the model for this article Integral Stats are defined for the BmSpotsWtLd and BmsToUnl queues. Their names are TrksWtLd and TrksWtUnld, respectively. Both Integral Stats have a divisor of 5. The screen shot below shows how to define Integral Stats for the BmSpotsWtLd queue:

When Integral Stats are defined, the simulation model report includes queue statistics from the perspective of the larger unit. These statistics are listed in the EZStrobe report under Time Weighted Collectors and includes:

Total Time, which matches simulation time, and can be accessed in formulas using the name of the Integral Stat followed by .TtlWgt (e.g., TrksWtLd.TtlWgt).
Current Content, which is the current content of the queue in terms of the larger unit, and can be accessed in formulas using the name of the Integral Stat (e.g., TrksWtLd).
Average, Standard Deviation, Minimum, and Maximum Content; all in terms of the larger unit, and can be accessed in formulas using the name of the Integral Stat followed by .AveVal, .SDVal, .MinVal and .MaxVal (e.g., TrksWtLd.AveVal).

In addition, the average waiting time from the perspective of the larger unit is listed in a separate table in the EZStrobe report. Starting with EZStrobe version 3.9, this can be accessed in formulas using the name of the Integral Stat followed by _AveWait (e.g., TrksWtLd_AveWait). Note that an underscore rather than a period separates the name of the Integral Stat and AveWait. In versions of EZStrobe prior to 3.9 there is no way to access this value directly in a formula. However, it can be easily calculated in terms of other available values. For example, the average waiting time for trucks to unload can be calculated using the following formula: TrksWtLd.AveVal*TrksWtLd.TtlWgt/(BmSpotsWtLd.TotCount/5).

With the addition of Integral Stats, the model described in this article provides identical results and statistics to the model described in the article for the multi-step activities with identical consecutive steps. The model described in this article, for non-identical or non-consecutive steps, can be obtained here. It has a seed and uses multiple random number streams so that it yields the exact same output as the other model (see EZStrobe Model Options for information on seed and streams).

The Non-Identical and Consecutive Issue

The model in this page supports multi-step activities when the time for each step need not be IID, or when the steps can be interrupted. However, the actual model presented does not have either characteristic. It was presented this way so that the model is able to produce the exact same result as the model used to illustrate identical and consecutive steps. In fact, the model presented should never be used when steps are identical and continuous since the other one is cleaner and more than twice as fast in execution.

Non IID cases can be represented by setting the duration of each step with a non IID formula. An example is when the activity exhibits a learning effect, where the time of the activity is some function of 1) the number of times it has taken place, 2) the number of steps that have already taken place, or 3) any other situation that dynamically changes the parameters used to determine the time of the step.

The case of Non consecutive steps will simply include other higher priority activities that may utilize one of the resources needed for a step. For example, a crane may be needed for high priority lift that will temporarily halt the loading of beams unto a flatbed until that high priority lift is complete.

The case of a variable number steps can be modeled by appropriately replacing the “>=5,5” in the link that precedes the Transport activity, with formulas that return the appropriate number of steps required to make a whole in the current situation.

Stroboscope Step by Step Installation

2011-02-12T18:49:00.000-05:00

Please download the Stroboscope Educational Setup and run it in your computer, you will see an open file security warning that looks like this:

Make sure you select “Run” in the screen above. After clicking “Run”, you will see a progress indicator for the extraction of the files, and then you will be asked to allow the setup program to make changes to your computer.

Under Vista and Windows 7, this question is in a “User Account Control” Window to which you should answer “Yes”:

Under Windows XP, this question is in a “Run As” Window. Make sure you grant the most authoritative permission when asked, by making sure you “run as administrator"; or if you are currently logged on as administrator, by un-checking the option to “protect my computer and data from unauthorized access”:

After granting authorization, regardless of the operating system you run, you will see a brief “preparing setup” message that will vanish on its own. You should then see the Welcome Screen of the Stroboscope Educational Setup Program, over a full screen background. The Welcome screen looks like this:

Once you click “Next”, the following screen will show up asking you to agree to the licensing terms:

You should click “Yes” unless you don’t agree to the terms and do not want to continue installing Stroboscope.

You will then see a dialog where you can indicate the location where you want to install Stroboscope:

If you want to accept the default, simply click “Next”. Otherwise you can click “Browse” to specify a different location and then click “Next”. After you click “Next” you will see a progress indicator, and after the files are installed you will get the “Setup Almost Complete” screen:

You should then click what is labeled as “Finish”, at which point the Registry Editor will ask you if you want to continue. You must answer “Yes”:

After you do so, you will get a confirmation from the Registry Editor:

After you click “OK” in the above dialog, you will get a registration screen that you need to accurately complete, and that looks like this:

If you do not have a key, just leave the key fields empty (not filled with spaces) and a key will be emailed to you after clicking “OK”. If you do have a key please enter it in the appropriate fields making sure you have no leading or trailing spaces in any field. If you have an Internet connection and your Firewall or your network is not blocking port 63714, you will see a brief Stroboscope banner. If port 63714 is blocked or you are not connected to the Internet, please click here for more information. If you did not enter a key, you will get the following notice:

After you dismiss the notice, wait a couple of minutes and then check your email for a message from Stroboscope containing your key. After you have your key, you should run the Stroboscope Integrated Development Environment from the Stroboscope Educational group within “All Programs” in the Windows start menu. When you do so, you will be greeted with the registration form, where you should enter your key and then click “OK”.

When you enter a valid key in the registration form,and press OK, you will get the following successful installation notice:

Press “OK” to acknowledge. At this point Stroboscope (as well as EZStrobe, ProbSched, and the Stroboscope Graphical User Interface) should be completely installed and ready to use.

Stroboscope is based upon work supported by the National Science Foundation under Grant No. 9733267. Any opinions, findings, and conclusions or recommendations are those of the author(s) and do not necessarily reflect the views of the National Science Foundation.

Stroboscope Debugger

2010-04-07T21:01:00.001-04:00

Prasant Rekapalli and I developed an interactive debugger for Stroboscope that can significantly assist with the debugging of Stroboscope simulation models.

You can get the debugger here.

To install, extract StroboState.dll from the zip file you downloaded above to the Program directory of the Stroboscope installation. This directory is by default at C:\Program Files\Julio C. Martinez\Stroboscope Educational\Program.

To use the debugger you need to add the following statement as the first one in your model:

LOADADDON StroboState.dll;

When you run a model that contains the above statement, you will see a window similar to the one below just before the simulation starts:

The title of the window contains the current step in the simulation, the current simulation time, and the next simulation time, all separated by the pipe “|” symbol.

Just below the title bar is a row containing tabs labeled activities, instances, queues, nodes, links, and parameters. The information shown in the panes below it depend on the tab currently selected.

The left information pane contains a hierarchical tree whose organization depends on the tab. When the activities tab is selected, for example, the top level is for the activities, the next level is for the current instances of the selected activity, and the third level is for the resources contained in the instance. If a resource is a compound resource it will contain another level below for the resources that it contains.

The top right information pane contains a series of properties and corresponding values about whatever is selected in the left information pane. This may include attributes as well as the current value of related statistics.

The bottom right information pane contains a list of events that can be checked or unchecked. Checking an event sets a breakpoint. The first three events listed (All Events, Before Time Advance, and After Time Advance) are global and independent of what tab or element in the left information pane is selected. “All Events” essentially triggers every possible breakpoint, allowing you to follow model execution step by step. Before and after time advance trigger breakpoints as indicated, just before the clock is advanced, and just after it is advanced. The remaining options trigger breakpoints corresponding to whatever is selected in the left information pane.

Below the information panes are dismiss, continue, execute, and evaluate buttons.

The Dismiss button allows you to continue the simulation without any further debugging.

The Continue button runs the simulation until the next breakpoint is encountered, at which point the debugger updates all its information. You are then allowed to inspect the state of your model and to set/unset any breakpoints. If you have no breakpoints set, then Continue and Dismiss are equivalent.

The execute button executes in Stroboscope the statement typed in the text box to its left. You should not include the ending semicolon. If the statement is executed correctly, the space to the right of the button will display “SUCCESS”, otherwise it will display “ERROR”.

The evaluate button will evaluate the expression typed in the text box to its left, and will display the result to its right. White space is allowed in the expression without the need to enclose it single quotes.

We hope this debugger helps you be more productive in your Strobing!

New system-maintained resource properties

2010-04-05T17:02:00.001-04:00

A new feature in Stroboscope since version 3.6

In addition to the TimeIn, ResNum and BirthTime resource properties, all resources now have the following properties:

WhereIs: returns the node, link or compound resource where the resource is currently located.

TopWhereIs: returns the node or link where the resource is currently located. Differs from WhereIs in cases where the resource is contained in a compound resource. This property returns the node or link where the resource is located.

This: returns the resource itself.

Filtering entire resource populations

2010-04-05T16:32:00.001-04:00

A new feature in Stroboscopoe since version 3.6

It is possible to apply a filter to the entire population of resources of a type using the following forms:

Filter.Property.{Count | Value | MinVal | MaxVal | SDVal | AveVal}

Value can be used when exactly one resource passes the filter. If the property is a SaveProp, you can assign a value to it. It is necessary to add '.Value' to differentiate from 'Filter.Property' which means the Property of the resource cursored by the Filter.

Controlling Stroboscope via Automation

2010-02-20T16:35:00.001-05:00

Stroboscope can be controlled from other applications using any programming language that supports Automation. The EZStrobe and ProbSched applications are such examples that control Stroboscope from within Visio using Visual Basic for Applications.

You can examine Stroboscope’s Automation interface by loading the Stroboscope Type Library (strbwin.tlb). In Visual Basic for Applications you can add strbwin.tlb as a reference, and then using the object explorer (typically pres F2 and then select the Stroboscope library) you can see the supported methods, arguments, and return values. Here is how the object explorer looks when opened in the VBA Window of Visio 2007:

Even though the “Stroboscope” type will be available in VBA as a valid type for dimensioning objects, it is best to dimension Stroboscope as a variable of type “Object”. The code below is an example that controls Stroboscope via VBA by sending a very small network, simulating it, and getting some output from it. It can be pasted as is into a Visio or Excel 2007 VBA module. To test it, execute the testStroboRun procedure:

Option Explicit
Public StroboApp As Object

'makes sure StroboApp is set to control
'Stroboscope
Public Function GetStrobo() As Object
    On Error Resume Next
    If (StroboApp Is Nothing) Then
        Set StroboApp = _
          CreateObject("Stroboscope.Document")
    End If
    If Err <> 0 Then
        MsgBox "Couldn't launch Stroboscope." _
          , vbOK + vbInformation, _
          "test Strobo"
        Err = 0
        Set GetStrobo = Nothing
    End If
    Set GetStrobo = StroboApp
End Function

'releases Stroboscope
Public Sub ReleaseStrobo()
Set StroboApp = Nothing
End Sub

Sub testStroboRun()
    'Get the Stroboscope object,
    'if not already acquired
    GetStrobo

    Dim nResult As Integer
    On Error Resume Next
    'set name of client running Stroboscope
    StroboApp.ClientVersion "test Strobo"
    If Err <> 0 Then
        nResult = -1
        GoTo CleanUp
    End If

    'The following two blocks define a very
    'simple network and runs it.
    'Any number of statements can be
    'sent in one call. It is in fact possible
    'to load an entire model from a *.str file
    'and pass it for execution as a single
    'string via the RunStatements method.
    'If running results in an error, the line
    'number of the error will return in nResult.
    'When no errors occur nResult will be
    'assigned zero.
    nResult = StroboApp.RunStatements( _
      "GENTYPE gen;QUEUE que gen;" _
      & "COMBI DoIt;DURATION DoIt Rnd[];" _
      & "LINK l1 que DoIt;LINK l2 DoIt que;")
    If nResult <> 0 Then GoTo CleanUp

    'just some more statements that actually do
    'something: initialize, simulate and report
    'the model
    nResult = StroboApp.RunStatements( _
      "INIT que 1;SIMULATEUNTIL SimTime>=10000;" _
      & "REPORT;")
    If nResult <> 0 Then GoTo CleanUp

    'we can get information from the model
    Dim st As Double
    st = StroboApp.EvaluateExpression("SimTime")
    MsgBox "The reported simulation end time " _
      & "was: " & st

'terminate model
StroboApp.EndModel

CleanUp:
    If nResult <> 0 Then
        MsgBox "STROBOSCOPE reported the " _
          & "following error: " _
          & StroboApp.geterrordescription() _
          & ".", , "test Strobo"
    End If

End Sub

CPMLevel

2009-10-04T17:49:00.001-04:00

CPMLevel is a Windows 3.1 CPM scheduling and resource leveling program based on an enhanced version of the Minimum Moment Method (MOM).

The original MOM algorithm is described in:

R. B. Harris, Precedence and Arrow Networking Techniques for Construction, J. Wiley & Sons, NY, NY, 1978.

CPMLevel animates histograms while leveling and allows manual activity displacements to explore various leveling strategies. CPMLevel was written in 1992 when personal computers were orders of magnitude slower. Back then, the animation of the leveling was slow enough to be observed. With today’s computers the animation is so fast that appears to be instantaneous. You may be able to enjoy the animation if you can slow down your computer or find an 80386 class computer to run it on.

To install CPMLevel you need to download CPMLevel.zip. Once you download this file you should extract its contents to a directory of your choice.

To run CPMLevel simply execute the file CPMLevel.exe. You may wish to create a shortcut or Program Manager icon for easy launching.

The files in the archive include a reference manual that explains the modified minimum moment method, a user’s guide that explains how to use the program, and several examples.

Learning Vitascope++

2009-10-04T12:18:00.001-04:00

Installed with Vitascope++ is a comprehensive tutorial which should be viewed using Microsoft Internet Explorer (other browsers do not show it properly). To launch the tutorial select “Tutorial” from the Vitascope++ program group. The tutorial consists of three parts. The first part is an introduction to Discrete-Event Simulation Based Virtual Reality (DESBasedVR) and the Vitascope++ system. The second part guides you to experience an interactive 3D animation driven by a robust discrete-event simulation. The third part is an introduction to the development of DESBasedVR environments.

Vitascope++ is fully documented in the system help file and in P. Rekapalli’s and V. Kamat’s Dissertations, the first two are installed along with Vitascope++. Tha latter is available here.

In addition, Vitascope++ includes several examples which can be used for learning.

Vitascope++ is based upon work supported by the National Science Foundation under Grants No. 0113890 and No. 0732560. Any opinions, findings, and conclusions or recommendations are those of the author(s) and do not necessarily reflect the views of the National Science Foundation.

Vitascope++ download and installation

2009-10-04T12:04:00.001-04:00

Prior to installing Vitascope++ you need to have the Microsoft Visual C++ Redistributable Package (x86) installed in your system. Chances are you may already have this, since it is required by numerous applications.

To install Vitascope++ simply download and execute the setup package, Vitascope++_Setup.EXE.

Please be sure to be connected to the Internet when you run Vitascope++_Setup. You will be required to register and to provide a key. If you do not have a key, please leave the key fields empty and a key will be emailed to the address you specify with registration.

If when you run Vitascope++ you get a message that the application has failed to start because its side-by-side configuration is incorrect, you can correct this error by installing the Microsoft Visual C++ Redistributable Package (x86).

Vitascope++

2009-10-04T11:59:00.001-04:00

Vitascope++ is a 3D animation system that can be used to animate previously simulated operations as well as concurrently animated operations where interaction with the animation can affect the remaining course of events in the simulation.

Vitascope++ moves and transforms 3D objects according to instructions that comply with its language specifications while maintaining a constant ratio of animated time to the time specified in the instructions.

When post processing, Vitascope++ reads a trace file that is typically written by discrete event simulation software as it runs. It is possible to navigate the 3D environment and to change the speed of the animation.

When running in concurrent mode, Vitascope++ is capable of affecting the state of the discrete-event simulation that drives it, making It possible to change the course of events in simulations by interacting with the animations. This makes it possible to create what are essentially Virtual Reality environments with the underlying logic defined by a sophisticated DES model where engineers can study/visualize the model's reaction to the events they introduce while experiencing the concurrently run animation.

Vitascope++ was developed in two stages. The first, called Vitascope (no plus plus), is based on VIneet Kamat’s Dissertation which was supervised by Julio C. Martinez at Virginia Tech. The second, called Vitascope++ (with the plus plus), is based on Prasant Rekapalli’s Dissertation which was supervised by Julio C. Martinez at Purdue University.

While you can download the original Vitascope (no plus plus, first stage only), the newer Vitascope++ improves on the original not only with regards to the concurrent and Virtual Reality capabilities that are not available in the former, but also in the performance of post processed animations.

Download and Install Vitascope++

Vita2D Download and Installation

2009-10-04T11:35:00.001-04:00

Vita2D is entirely contained in a single file, Vita2D.vss, which is included along with several others in this zip archive. Vita2D.vss should be extracted to a directory listed in the Visio ‘Stencils’ path (which can be specified using Tools->Options and then FilePaths in the Advanced Tab). In addition, in Visio 2003 the security level should be set at the most to ‘medium’ (Tools->Options and then Macro Security in the Security tab); in Visio 2007 the directory where it is located should be declared a ‘trusted location’ (Tools->Trust Center and then Trusted Locations in the left hand column). If you have a working Stroboscope installation, the Program/GUI directory under the main Stroboscope directory complies with these requirements, and the quickest way to install Vita2D is to copy it to that directory.

The example files and documentation that come along with Vita2D can be extracted to a directory of your choice. These files include a tutorial and guide (Vita2D.pdf), a Stroboscope model that can generate the complete example discussed in the tutorial (Vita2DExampleModel.str), a pre-generated trace file that can readily be used to experience an animation (Vita2DExample_10Trucks.vtf2d), the Visio drawing file required for the animation (Vita2DExampleAnimation.vsd), and the pair Demo.vsd and Demo.vtf2D which make up a hand-written animation that demonstrates some of Vita2D’s capabilities.

Vita2D

2009-10-04T11:23:00.001-04:00

Vita2D is a post-processing animator hosted on Microsoft Visio. It creates, moves, and modifies objects in a drawing according to instructions in a trace file that is written according to the Vita2D language specification. Vita2D attempts to maintain a constant
ratio of animated time to the time specified in the instructions.

Vita2D trace files are typically generated by discrete-event simulations when they run. The example included with Vita2D uses a Stroboscope simulation model, but any system can be used as long as it is capable of writing instructions to a file during simulation. It is also possible to create some short animations by typing directly the trace file instructions. The Demo animation included with Vita2D is an example of this.

Vita2D was written in order to quickly animate simulations without spending time in 3D modeling, and by working with a streamlined and polished development environment that is conducive to quick productivity – unlike Proof Animation (Wolverine Software 1995), which uses a development environment that is unique to it. Some elemental knowledge of Visio ShapeSheet technology is needed to create animations.

Vita2D Download and Installation

ProbSched

2009-10-04T11:18:00.001-04:00

ProbSched is a probabilistic scheduling package that uses Stroboscope as its engine and Visio as its Graphical User Interface. ProbSched allows the definition of CPM networks where the cost and duration of each activity can be defined probabilistically. ProbSched produces graphical output to indicate the criticality of each activity and statistics of the early and late times and floats of each activity and the project.

ProbSched is installed with Stroboscope and can be launched by selecting ProbSched from the Stroboscope program group.

ProbSched is based upon work supported by the National Science Foundation under Grant No. 9733267. Any opinions, findings, and conclusions or recommendations are those of the author(s) and do not necessarily reflect the views of the National Science Foundation.

Cannot launch or open Stroboscope

2009-10-04T11:09:00.001-04:00

The most likely cause of this problem is a faulty installation. The later versions of Stroboscope have a significantly improved setup program that prevents a faulty installation from taking place. If your version of Stroboscope is lower than 3.8, then download and install the latest one.

For the sake of those who are curious, below is an explanation and solution to the problem for those with older versions of Stroboscope.

In some cases, particularly when the Stroboscope installation instructions are not followed carefully the first time, you may get an error message from EZStrobe or the Stroboscope GUI indicating that it could not launch Stroboscope or open it for automation.

To correct this problem, download StroboAutom.zip and extract the file STROBOAUTOM.VBS to the Stroboscope Program directory. By default this directory is at “C:\Program Files\Julio C. Martinez\Stroboscope Educational\Program”. With some zip extraction utilities you may have trouble extracting the file directly to the Stroboscope Program directory due to permission issues. In these cases, please extract StroboAutom.vbs to a temporary location and then copy it from there to the Stroboscope Program directory. After it is downloaded to that directory, execute it by double-clicking. Make sure you answer positively to all prompts – you should see several.

Under Vista and Windows 7, you will not be able to proceed unless you answer positively to the question that asks whether you want to allow changes to be made to your computer. Under Windows XP, make sure you grant the most authoritative permission when asked, by making sure you “run as administrator"; or if you are currently logged on as administrator, by un-checking the option to “protect my computer and data from unauthorized access”:

Also make sure that you respond to the registry editor, which may be blinking in the taskbar to catch your attention.

EZStrobe

2009-10-04T10:20:00.001-04:00

EZStrobe is an entirely graphical simulation system based on extended and annotated Activity Cycle Diagrams that uses Three-Phase Activity Scanning. Although EZStrobe uses Stroboscope as its engine, EZStrobe is not Stroboscope. You can learn how to use EZStrobe effectively without having to learn Stroboscope or having to use Stroboscope directly.

EZStrobe is ideal as a first general purpose simulation tool because it requires no programming. EZStrobe is capable of modeling complex operations as long as it is not necessary to access the properties or state of resources, or to differentiate among them.

EZStrobe is installed automatically when Stroboscope is installed.

Once you have installed Stroboscope, you can get started at the Learning EZStrobe page.

Learning Stroboscope

2009-10-04T10:01:00.001-04:00

Stroboscope is an advanced simulation language suitable for modeling very complex operations in many areas of application. It is strongly advised, but not required, to first learn and master EZStrobe.

The best way to lean Stroboscope is by carefully reading J.C. Martinez’ Dissertation, trying the code that is presented in the Stroboscope IDE, and experimenting with concepts as they are introduced. J.C. Martinez’ Dissertation is installed in PDF format with Stroboscope and available under the entry “The Stroboscope Simulation Language” in the Stroboscope shortcuts created during installation. That document describes Stroboscope as it existed in January 1996. The Stroboscope language has been significantly enhanced since then with even more advanced capabilities. These capabilities are documented in summary form along with the original Stroboscope in the “Stroboscope Quick Reference Guide” which is also installed as a PDF with Stroboscope.

In addition, several examples documented in publications are also available and installed with Stroboscope. These are located in Examples –> Stroboscope in the Stroboscope program group.

Stroboscope: Communication problems with the License Server

2009-10-04T09:29:00.001-04:00

Stroboscope uses a licensing scheme that requires validation over the Internet on first use, and sporadically thereafter (500 runs or one year since last validation). If upon startup Stroboscope detects that it is connected to the Internet, but that access to the License Servers is blocked, it will not run.

This may happen if you have a firewall that prevents Stroboscope from initiating Internet communications. To solve the problem in this case, make sure you add the Stroboscope executable to the list of exceptions in your Firewall. The Stroboscope executable is STRBWIN.EXE and is located in the PROGRAM subdirectory under the main Stroboscope installation directory.

Communication may also be blocked at the network level. In this case, you need to contact your network administrator to allow traffic to licenseserver.ezstrobe.com and licenseserverbackup.ezstrobe.com via port 63714.

Installing Stroboscope

2009-10-04T06:23:00.004-04:00

Stroboscope runs under Microsoft Windows XP or later operating systems. The default user interface for Stroboscope is an Integrated Development Environment (IDE) similar to those used by most programming languages under Windows. Simulation models are typed using the text editor built into the IDE.

A Graphical User Interface (GUI) as well as the EZStrobe and ProbSched systems are also included with Stroboscope. These tools require Microsoft Visio 2000 or later. If you plan to use these (strongly recommended), please install Visio prior to installing Stroboscope.

Prior to installing Stroboscope you need to have the Microsoft Visual C++ 2008 SP1 Redistributable Package (x86) installed in your system. Chances are you may already have this, since it is required by numerous applications.

To install Stroboscope simply download and execute the setup package, Strobosc.exe.

Please be sure to be connected to the Internet when you run Strobosc. You will be required to register and to provide a key. If you do not have a key, please leave the key fields empty and a key will be emailed to the address you specify with registration.

If when you run Stroboscope you get a message that the application has failed to start because its side-by-side configuration is incorrect, you can correct this error by installing the Microsoft Visual C++ 2008 SP1 Redistributable Package (x86).

Stroboscope

2009-10-03T22:11:00.007-04:00

Stroboscope is a simulation programming language and system for modeling complex processes in a variety of areas ranging from construction, to manufacturing, to hospital operations.

The name STROBOSCOPE, an acronym for STate- and ResOurce-Based Simulation of COnstruction ProcEsses, reflects the system's major design objective: the ability to make complex dynamic decisions (and thus control the simulation at run-time) based on the simulation system state and the characteristics, attributes, and state of resources. Unlike other simulation systems, Stroboscope is based on three-phase activity scanning and not process interaction. The activity-scanning simulation paradigm makes Stroboscope better-suited for modeling complex resource interactions such as those that characterize cyclic operations where no distinction is made between resources that serve (servers or scarce resources) and those served (customers or moving entities). Stroboscope simulation models use a graphical network-based representation similar to activity cycle diagrams.

Included with Stroboscope, are the EZStrobe and ProbSched systems. Although these two systems require Stroboscope, there is no need to learn Stroboscope to use them.

Download and Installation Instructions

Welcome

2009-10-03T21:46:00.004-04:00

Welcome to EZStrobe.com. This site features software authored or co-authored by Julio C. Martinez. Stroboscope and CPMLevel are co-authored with Photios G. Ioannou. Vitascope++ is co-authored with Vineet R. Kamat and Prasant V. Rekapalli. From here you will be able to download, find installation instructions, solutions to common problems, examples, and just about anything related to the software that may be useful.

To navigate this site, use the hierarchical Site Navigation control at the top of the right column.

The software featured here includes:

Stroboscope – an advanced discrete event simulation programming language and system based on Three-Phase Activity Scanning and extended Activity Cycle Diagrams.
EZStrobe – a simpler discrete-event simulation system suitable for learning and modeling processes and operations that do not require the explicit identification of resources.
ProbSched - a probabilistic scheduling package that uses Stroboscope as its engine and Visio as its Graphical User Interface.
Vita2D – a 2D animation system hosted on Microsoft Visio that can be used to animate previously simulated operations.
Vitascope++ – a 3D animation system that can be used to animate previously simulated operations as well as concurrently animated operations where interaction with the animation can affect the remaining course of events in the simulation.
CPMLevel – a CPM scheduling and resource leveling program based on an enhanced version of the Minimum Moment Method.

Thank you for visiting!

Stroboscope, EZStrobe, ProbSched, Vitascope and Vitascope++ are based upon work supported by the National Science Foundation under Grants No. 9733267, No. 0113890, and No. 0732560. Any opinions, findings, and conclusions or recommendations are those of the author(s) and do not necessarily reflect the views of the National Science Foundation.