Excel's Formula - sisman

Chapter 16: Intentional Circular References 421
If you have all workbooks closed and you create a new workbook, the new workbook
uses the same Calculation mode as the last closed workbook. The exception is if you create
the workbook from a template, the workbook uses the calculation mode specified in
the template.
If the mode of calculation in a workbook changes and you save the file, the current mode
of calculation saves with the workbook.
Bottom line? When you open a workbook that uses iteration, there is no guarantee that the setting
saved with your workbook will be the setting that is in effect when you open the workbook.
When the Enable Iterative Calculation setting is in effect, Excel will never display the
Circular References warning dialog box and will not display the Circular References
message in the status bar. Therefore, you may create an unintentional circular reference
and not even know about it.
Circular Reference Examples
Following are a few more examples of using intentional circular references. They demonstrate
creating circular references for entering unique random numbers, solving a recursive equation,
solving simultaneous equations, and animating a chart.
For these examples to work properly, the Enable Iterative Calculation setting must be
in effect. Choose Excel Options, navigate to the Formulas section, and mark the Enable
Iterative Calculation check box.
Generating unique random integers
This example demonstrates how to take advantage of a circular reference to generate unique
(nonduplicated) random integers in a range. The worksheet in Figure 16-5 generates 15 random
integers between the values specified in cells E1 and E2.
Column B contains formulas that count the number of times a particular number appears in the
range A1:A15 (named RandomNumbers). For example, the formula in cell B1 follows. This formula
displays the number of times the value in cell A1 appears in the RandomNumbers range:
=COUNTIF(RandomNumbers,A1)
Cell B17, named Dupes, displays the number of duplicated values using this formula:
=SUM(B1:B15)-COUNTA(B1:B15)