Sim Gen node (SPSS Modeler)

Sim Gen node

The Simulation Generate node provides an easy way to generate simulated data. You can use the node either by specifying statistical distributions without historical data, or by using the distributions obtained automatically from running a Simulation Fitting node on existing historical data. Generating simulated data is useful when you want to evaluate the outcome of a predictive model in the presence of uncertainty in the model inputs.

Creating data without historical data

The Simulation Generate node is available from the nodes palette and can be added directly to your flow.

Click the Import tab of the nodes palette.
Drag or double-click the Sim Gen node to add it to your flow.
Double-click the node to open its properties and specify fields, storage types, statistical distributions, and distribution parameters.

Note: After you add a Simulation Generate node to your flow it starts blank, with no fields and no distribution information. You can use the blank node to create simulated data without historical data.

Generating simulated data using existing historical data

You can also create a Simulation Generate node by running a Simulation Fitting terminal node:

Hover over a Sim Fit node in your flow and click the Run icon .
The Simulation Generate node appears on the flow canvas with an update link to the Simulation Fitting node.
When generated, the Simulation Generate node inherits all the fields, storage types, and statistical distribution information from the Simulation Fitting node.

Defining an update link to a Sim Fit node

You can create a link between a Simulation Generate node and a Simulation Fitting node. This is useful if you want to update one or more fields with the information of the best fitting distribution, determined by fitting to historical data.

Right-click the Simulation Generate node and choose Define Update Link.
Click another node. If this node is a Simulation Fitting node, a link is made. If this node is not a Simulation Fitting node, no link is made.

When you use a Simulation Fitting node to update a linked Simulation Generate node, the result depends on whether the same fields are present in both nodes, and if the fields are unlocked in the Simulation Generate node. The results of updating a Simulation Fitting node are shown in the following table.

Table 1. Results of updating a Simulation Fitting node
	Field in Simulation	Fitting node
Field in Simulation Generate node	Present	Missing
Present and unlocked.	Field is overwritten.	Field is deleted.
Missing.	Field is added.	No change.
Present and locked.	The distribution of the field is not overwritten. The information in the Fit Details dialog box and the correlations are updated.	The field is not overwritten. The correlations are set to zero.
Do not clear Min/Max when refitting option is selected.	The field is overwritten, apart from	the values in the Min, Max column.
Do not recalculate correlations when refitting option is selected.	If the field is unlocked, it is overwritten.	The correlations are not overwritten.

Removing an update link to a Sim Fit node

You can remove a link between a Simulation Generate node and a Simulation Fitting node by right-clicking the Simulation Generate node and selecting Remove Update Link.