Utility Function Status

When a utility function is created in DEXi, it is completely undefined at first: all cells in Function Editor contain the undefined value ‘*’. When you edit the function, you usually assign values to more and more cells and the function becomes more and more defined. Usually, the goal is to completely define the function, that is, to precisely specify all cell values.

DEXi uses two measures of function definition, which are both displayed as status/progress indicators on Model Page and in Function Editor.

The first measure is called entered rules ratio. This is a ratio between the number of entered rules (that is, cell values defined by you) and the total number of rules (function size).

The second measure, determination, is somewhat more complex, but better. It takes into the account that, in general, cell values are intervals rather than single values. A cell is 100% determined if it is assigned a single value, and is 0% determined if it is completely undefined, that is, it contains the complete interval of values (denoted ‘*’). For smaller intervals, intermediate values are calculated proportionally.

A function is fully determined when all its cells - both entered and non-entered - are 100% determined. This is in general achievable with less than 100% entered rules due to DEXi’s handling of non-entered values. Therefore, when editing a function, the primary aim is to make it 100% determined, regardless on the ratio of entered rules.

The display of utility function status also includes a frequency distribution of function values, shown in square brackets. For instance, ‘[high:5,medium:1,low:3]’ denotes that five decision rules map to the value ‘high’, one rule to ‘medium’ and three to ‘low’. For functions that contain intervals, the sum of frequencies is greater than the total number of rules.