Configure Time Series

Once a time series model has been selected it can be configured using the Configuration Panel on the left side of the Define Time Series window. All changes to the model function made through this panel will be reflected immediately in the Formula Bar. The Configuration Panel consists of three main sections:

Figure 1 - Time Series Parameters

  • Time Series - Primary settings for the time series model function (Figure 1, right); these include the model being used and the parameter values, e.g. mean (µ), volatility (σ), autoregressive coefficient (a1), and initial value (Y0) for an AR(1) time series model (Figure 1, right).
  • Transformations - Apply any transformation to define a non-stationary time series by adding trend and/or seasonality. See Time Series Transformations for more information.
  • General - Define, or update, the Excel range for the time series, provide a name, and set synchronization.

Throughout the @RISK windows, the new More button ( ) indicates a menu or other window for selecting configuration options. For example, in the Define Time Series window the More button will open the 'Select a Model' window, where a different time series model can be selected.

Time Series Parameters

The mathematical definition of a time series function is set in the Time Series section.

  • Model Field - This field lists the time series model currently in use. Clicking the More button will open the Select Model window, where a new time series model can be selected.
  • Parameter Values - These fields detail the specific values being used in the time series; in addition to numeric values, parameter values can also use references to other Excel cells (including cells containing formulas or other @RISK distributions) enabling the creation of complex models. The number of available parameters will change depending on the time series model being used.

Transformation Properties

Figure 2 - Time Series Transformations

The Transfomation fields (Figure 2, right) are used to apply Transformation to the data values generated for a time series model. See Time Series Transformations for a complete discussion on using transformations.

General Configurations

The final section of the Configuration Panel is the General settings for the time series model. These settings control the number of elements in the series, the name of the series, and how the time series model results should synchronize.

  • Series Range - The range of cells that will include the time series model function; the default number of cells is 24, but this can be changed by modifying the Series range.

  • Please note: It is recommended that a Series Range be limited to 50,000 cells or less. When a Series Range exceeds 50,000 cells recalculation of the workbook may slow or the application may run out of memory.

  • Name - The name for the time series model. The Name value will appear as the header for the graph, as well as in the Name column of the Model Window.
  • Synchronization - Define if and how the time series should be synchronized to existing data - no synchronization, on the last value, or on the first value. See the @RISK function RiskTSSync for more information.

  • Please note: It is recommended that a Syncronization range be limited to 250,000 cells or less. When a Syncronization range exceeds 250,000 cells the Define Time Series dialog may refresh slowly or the application may run out of memory.