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HomeTechniques and Tips@RISK Simulation: Numerical ResultsSome Iterations Show Error in Data Window. What Can I Do?

6.35. Some Iterations Show Error in Data Window. What Can I Do?

Applies to: @RISK for Excel 5.x–7.x

When I run my simulation and click the x-subscript-i icon to check the @RISK Data window, I see "Error" for some iterations in one or more outputs. What does that mean? There are no #N/A or #VALUE errors in my workbook.

In the @RISK Data window, each row is an iteration and each column is an @RISK input or output. "Error" in the @RISK Data window means that the formula in that cell (column heading) has an Excel error in that iteration (row heading). But the problem may or may not be in the formula in that cell. It might in be a formula in a cell that is referenced by that cell. (In Excel, when any cell has an error status, all the cells that use it in formulas share that error status.)

How can you have errors in particular iterations when there are no errors in the worksheet as displayed when a simulation is not running? For example, suppose you have RiskNormal(10,3) in one cell, and in another cell you take the square root of the first cell. The static value of the RiskNormal( ) is 10, so when a simulation is not running you won't see any error. But during an iteration, occasionally the RiskNormal( ) will return a negative value, and the square root of a negative value returns a #NUM error. If the cell that contains the square-root function, or any cell that depends on it, is an @RISK output, then you will see an error in the Simulation Data window for that iteration.

To find the source of the error:

In the Results section of the @RISK ribbon, click the Simulation Data icon, the small icon showing x-subscript-i. The @RISK Data window opens, showing all outputs in columns, and then all inputs. Locate your output, then an Error indication. Click on it, and then click the footprint or shoeprint icon at the bottom of the window. (The tool tip, if you hover your mouse over the icon, is "Update Excel with values from the selected iteration". If the button is grayed out, see Footprint Button Grayed Out.)

@RISK will put your workbook into the state it was in during that iteration. Then you can check the error cell and trace back through the formulas till you find the source of the error. (You may need to minimize the @RISK Data window, or grab its title bar with your mouse and move it out of your way.) You can click on other iterations in the @RISK Data window to display other iterations of the workbook.

(Actually, @RISK sets all inputs to the values they had during that iteration, then recalculates the workbook to let Excel fill in the outputs. If shoeprint mode shows different output values from the ones shown in the Data Window for the same iteration, see Random Number Generation, Seed Values, and Reproducibility.)

When you have found the problem, click the footprint icon again to return the workbook to its normal state, or simply close the Data Window.

See also:

Additional keywords: Shoeprint mode, footprint mode

Last edited: 2019-02-15

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