Help modeling probability distribution for number of consecutive totes

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Lambert asked May 5, '22 Julie Weller commented Aug 1, '23

Help modeling probability distribution for number of consecutive totes

Hi, I am trying to model the induction of totes into a conveyor based on a forecasted probability (weight).

So far I am using the following empirical distribution:

Now, I would like to add in variability in terms of the number of consecutive totes for the same arc that go into the conveyor.

In other words, I would like to have parameters that increase/decrease the probability of having more/less consecutive totes for the same arc:

for example:

1-4-6-1-3-1-6 vs 1-1-1-4-6-6-3

does anyone have any ideas on how to model this?

In my head the expected behavior would be something like this:

Thank you in advance,

Lambert

Software Version:

FlexSim 22.1.1

probability distribution

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Answer 1 · 2022-05-05T11:34:50Z

Jason Lightfoot answered May 5, '22 Julie Weller commented Aug 1, '23

The weight give the increased chance of having two consecutive totes on the same arc if you're sampling for each tote.

If you're sampling for a each slug of totes going to an arc, then you can do that in a seperate lookup but then sample less frequently from the the empirical distribution. That then mean the empirical should represent the spread of consecutave totes and not the total spread of totes, meaning you data should be changed to reflect that (if it's the spread of totes currently).

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Lambert commented · May 05, 2022 at 12:53 PM

Thanks Jason

"The weight give the increased chance of having two consecutive totes on the same arc if you're sampling for each tote. "

This makes sense.

How can I then add some variability to the weights defined in the empirical distribution attached to the source of totes?

for example, for arc 1, 15 plus/minus a random probability distribution

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Lambert Lambert commented · May 05, 2022 at 07:09 PM

@Jason Lightfoot

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Jason Lightfoot ♦♦ Lambert commented · Jul 26, 2023 at 10:59 AM

Sorry we missed this.

If you comment and then accept an answer as was the case here - it can disappear from our tracking system. While you require follow-up please do not accept the answer after a follow-up question.

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Julie Weller Lambert commented · Aug 01, 2023 at 05:01 PM

Are you still struggling with this follow up question? If so would you want to post it as a new question? Thanks in advance!

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Answer 2 · 2022-05-09T05:48:42Z

Lambert answered May 9, '22 Felix Möhlmann commented Jul 27, '23

Hi good morning,

could anyone tell me how to add some variability to a Empirical Distribution?

I'd like that with each replication of the simulation it takes different values.

For example, for Arc 1, instead of a fixed 15 weight, i'd like to use Normal (15, 2) that varies with each replication

Thank you in advance,

Lambert

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Felix Möhlmann commented · May 09, 2022 at 07:14 AM

You could set the distribution weights in the model reset trigger and use a global table to store the respective distributions (make sure to 'Assign FlexScript Data' to the table cells).

// Reference to distribution table and source table
treenode distributionBundle = Model.find("Tools/EmpiricalDistributions/EmpiricalDistribution1>variables/data");
Table weightsTable = Table("EmpDistWeights");

// Create array of weights based on table
Array weights = Array(weightsTable.numRows);
double sum = 0;
for(int index = 1; index <= weights.length; index++)
{
    weights[index] = weightsTable[index][1];
    sum += weights[index];
}

// Scale to 100% and assign to distribution
for(int index = 1; index <= weights.length; index++)
{
    weights[index] = weights[index]/sum*100;
    setbundlevalue(distributionBundle, index-1, 1, weights[index]);
}

This will of course only yield different results, if the 'Repeat Random Streams' option is inactive or for different replications of the experimenter.

Variable_EmpDistribution_fm.fsm

Please consider posting a new question the next time, if it doesn't directly relate to the topic of the previous one.

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variable-empdistribution-fm.fsm (35.7 KiB)

Lambert Felix Möhlmann commented · May 09, 2022 at 10:08 AM

@Felix Möhlmann

Thank you Felix, it seems to work fine except for some totes that do not get anything assigned (arc remains blank)

do you know what can be the reason?

updated: seems to be related with the decimal points.

now when I click in generate samples, i get the following error:

exception: FlexScript exception: Invalid row identifier forVIEW:/active/EmpiricalDistributionProperties2700133680/GenerateSamples/popup2699292528/BarChart>variables/dumpData at VIEW:/active/EmpiricalDistributionProperties2700133680/GenerateSamples/popup2699292528/BarChart>eventfunctions/getData c: VIEW:/active/EmpiricalDistributionProperties2700133680/GenerateSamples/popup2699292528/BarChart

thank you

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Felix Möhlmann Lambert commented · May 09, 2022 at 05:05 PM

Looks like a bug. I get the same with a fresh model/distribution when changing the data type around a lot.

It seems like the Variant returned by Empirical().get() is not always interpreted as the correct type when assigning it to the bundle that holds the sample data.

If I run the same code but cast the Variant as the respective type (...as(double)) it works consistently.

For now I can only offer the workaround to test the distribution 'manually' by writing sample data to a global table, link that to a calculated table and plot it in a dashboard chart.

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