Excel supports control of iterative calculations through the calculation options dialog box.Īfter marking cells as dirty, when a recalculation is next done, Excel reevaluates the contents of each dirty cell in the order dictated by the calculation chain. For example, you might want to run an iterative calculation where the starting point for the next iteration is the result of the previous iteration. In some cases, you might deliberately want this condition to exist. This is usually an error condition that the user must fix, and Excel provides very helpful graphical and navigational tools to help the user to find the source of the circular dependency. If a cell depends, directly or indirectly, on itself, Excel detects the circular reference and warns the user.
All direct and indirect dependents are marked as dirty so that if B1 depends on A1, and C1 depends on B1, when A1 is changed, both B1 and C1 are marked as dirty.
Cells that are marked in this way are known as dirty. When new data or new formulas are entered, Excel marks all the cells that depend on that new data as needing recalculation. When a structural change is made to a workbook, for example, when a new formula is entered, Excel reconstructs the dependency tree and calculation chain. For this reason, calculation times can often improve in a worksheet that has just been opened in the first few calculation cycles. In this case, the cell that is being calculated and its dependents are moved down the chain.
During recalculation, Excel revises this chain if it comes across a formula that depends on a cell that has not yet been calculated. The calculation chain lists all the cells that contain formulas in the order in which they should be calculated. From this tree, Excel constructs a calculation chain. The dependency tree informs Excel about which cells depend on which others, or equivalently, which cells are precedents for which others. The calculation of worksheets in Excel can be viewed as a three-stage process: Therefore the phrase "the user" also means "the user, or a command or process started by the user." Dependence, Dirty Cells, and Recalculated Cells The user runs the command, or does something to cause the command to run so that it is still considered a user action. This topic does not distinguish between the user directly pressing a key or clicking the mouse, and those tasks being done by a command or macro.
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