What is the algorithm used by Auto Fill in Excel?
For example, when I enter the numbers 3,4,5,7,8 into a column and then use Auto Fill, I get the following result:
3 4 5 7 8 9.3 10.6 11.9 13.2 14.5 15.8 17.1 18.4
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Excel uses its Linear Trend approach when you auto-fill. This employs the least-squares method algorithm.
This is the same algorithm used by the
TREND() function as seen demonstrated below:
Enter the following formula in
C6 and ctrl-enter/copy-paste/fill-down into the rest of the column:
Below is a chart showing the trend line that the new values fall on.
The least-squares method creates a "best fit" line for the original data points. The new data points are essentially extracted from this line.