Randomize initial TSD within state specific range (VDDT

[maxwahlberg]

I’m working with some VDDT models where I have applied minimum time since disturbance values for some probabilistic transitions with high probability. When setting initial conditions in the Run Settings dialog, I am given the option to “randomize initial TSD to a maximum of…”. However, it seems I can only set one maximum TSD value, which is then used to randomize a range for all states. This is problematic for me because I have different minimum TSD values for each state, and applying one range of TSD values to the initial seed means that I start with some TSD values that are outside the realistic range for a given state (and thus “push” a transition either earlier or later than would be applied otherwise.) Is there any way to randomize initial TSD so that it applies a random number between 0 and the minimum TSD value for each state individually? (Similar to the way initial ages are normalized within a range in at the beginning of a run.)
Thanks,
Max

[leonardo-frid]

Hi Max,

 

In VDDT you can set TSD values by State Class for individual records in the Initial Conditions screen.  This is described on page 62 of the VDDT user manual.  If you want these values to be randomized you will need to do the randomization outside of VDDT and then create multiple records for each state class, each with different TSD values.  At the moment we are no longer developing VDDT but the ability to randomize by state class could be an enhancement we consider in the future for Path / ST-Sim.

 

Regards,

Leonardo

[maxwahlberg]

Thanks for the prompt response Leonardo.
This is as I expected, but I figured I could ask. I have played with adding multiple records for each state class, but pragmatically I would only load a finite number of records for each state. In this way, I will wind up with a series of artificial cohorts (one for each record entered) each experiencing batch transitions with high probability when their respective TSD value is hit.
Out of curiosity, does Path allow for the importation of initial conditions from an Excel or CSV file? If so, is there a limit to the number of records you can have for each model state (in the initial conditions)?
Thanks,
Max

[leonardo-frid]

Hi Max,

 

Yes, Path and ST-Sim both allow for loading initial conditions from excel.  The limit would be the number of records possilbe on the version of excel you are working with so if you have excel 2007 or later that would be 1 million records.

 

Note that at the moment. TSD is not set for individual records in the initial conditions property for Path or  ST-Sim.  You can randomize TSD by stratum.  In the future it is conceivable that your suggestion of randomizing by state class could be implemented or also the ability to specify TSD values for individual records in the initial conditions property.  Note that in Path and ST-Sim TSD is referred to as Time Since Transition (TST).

 

Regards,

Leonardo

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