How to set a dynamic starting condition for a reservoir object?

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Page Weil

• January 23, 2026 00:41

I have a reservoir model where I want to be able to select from different starting condition options:

• Start empty
• Start full
• Start using the historical contents on the day the simulation is kicked off

I have created a data element to select the source type, and I have values for all options in different data or timeseries elements. However, when I try to run the model I get the following error:

The following error was found in the model.  To continue, you must resolve this error.

The initial value input definition for 'Initial Quantity' is invalid. The input only accepts constant values or references to static elements and local properties (e.g. a Data element that specifies a local value of 5m, or a static local property such as Realization), but can not reference element [DATA ELEMENT].  Note that outputs of Subsystem Containers can not be used for initial values.

I want to set this value once at the beginning of the timestep. Do you have any suggestions for how to assign this starting value dynamically? 

Thanks in advance

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  Jason

  • January 23, 2026 17:36
  • Edited

  Page,

  Good question. This type of thing is done for carryover storage in Monte Carlo simulation models where we simulate a time period shorter than the reservoir's cycle time. Please have a look at this example that use Discrete Change elements to reset the value at time = 0 d. I think this is the approach that could work in your case. Let me know if that helps.
  
  Output Feedback to Input Between Realizations – GoldSim Help Center
  
  -Jason

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  Page Weil

  • January 23, 2026 18:26

  Okay, this looks like it is what I want. One issue though is that I want to define the discrete change as coming from a vector (I have about 20 different reservoir accounts I want to set all at once). When I try to set the Discrete Change element to a Vector and use it on the reservoir, I get this error:

  

  Is there a workaround to let me set all reservoir starting contents in some kind of vector format and then refer to them based on their index (rather than creating 20 elements to set the discrete change)?

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  Jason

  • January 23, 2026 20:20

  Page,

  If the storage element is a scalar, then the Discrete Change should also be a scalar (not vector). Your options appear to be that you create 1 Discrete Change element for each Pool element (my preference in this case). Or use a vector type Reservoir element for your 20 reservoir accounts and then the discrete change can be a vector of the same size. 

  Does that help?

  -Jason

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