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Adding an outbreak

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    I am running some non-spatial models and I have an outbreak with the following criteria that I am trying to add to Syncrosim:
    1) Interval between outbreaks (example: an outbreak can occur every 35 to 45 years)
    2) Outbreak duration (example: an outbreak can last 7-9 years)
    3) Outbreak multiplier (example: receive a value of 1 during an outbreak, otherwise have a multiplier of 0).

    I can create a file that does all of these things, but it requires an individual record for each strata, iteration, and timestep, resulting in millions of records. I am sure there is a better/more efficient way to do this in Syncrosim but I cannot quite figure it out. Do you have a non-spatial Syncrosim example you are comfortable sharing where you incorporated all of these criteria (system and actual transition agent doesn’t matter)? If not, might you explain where/how I can incorporate an outbreak duration?

    Thanks in advance for any help,


    Hi Josh,

    If your outbreaks are correlated between strata, I think the best you could do is create an external variable for outbreak years (0/1) and define a value for this for every iteration/timestep. This would reduce the number of records you have to define somewhat but not entirely. To do it, here are the steps I would follow:
    1. Create an external variable under Project Properties: “Outbreak Year”
    2. Create a Distribution Type under Project Properties: “Outbreak Multiplier”
    3. Under Scenario Properties | External Variables:Define a value for each timestep and iteration that includes the 0 values for non outbreak years and the 1 values for outbreak years.
    4. Under Scenario Properties | Distributions you would then define two Distribution records for each stratum that specify the “Outbreak Multiplier” when your “Outbreak Year” value is 0 and the other when it is 1. Set the Sampling frequency to “every timestep”.
    5. Under Scenario Properties | Transitions – Multipliers set your multipliers to come from the “Outbreak Multiplier” Multiplier Distribution. Set the Sampling frequency to “every timestep”.

    Hope that helps!


    One additional note is that for outbreak/non-outbreak years in your external variable, you don’t need a record for every timestep. For example if you had a 7 year outbreak starting in 2020 followed by a 20 year non-outbreak period your external variable records would be:
    Iteration, Timestep, Value
    1, 2020, 1
    1, 2027, 0
    1, 2047, 1

    This will also greatly reduce the number of records that you need.



    Thanks for the explanation, Leonardo. Unless I am missing something, I think the main limitation of the approach you describe are:

    1) I would still need to use some sort of random number generator to figure out when an outbreak would occur within an iteration (but I think I could work around this), and
    2) The approach seems a bit time consuming when each iteration contains hundreds to thousands of timesteps, like in a natural/historical range of variability analysis.

    But I look forward to using the approach you describe in shorter runs down the road. Again, thanks for making the time to answer my original question.


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