A few weeks ago a client contacted us about the XLeratorDB LINEST function and whether or not it could a handle a linear system where the number of rows was less than the number of columns. I told him that in such a case the LINEST function would generate an error message because it requires that the number of rows to at least be equal to the number of regressors.
He then told me that he could do it in Excel, so I asked him to send me his workbook, which he did. After reviewing his workbook I discovered that his particular example wasn’t actually doing what he thought it was doing and that he actually did have a linear system that satisfied the requirements with regards to the number of rows and the number of regressors. Further, XLeratorDB and Excel produced identical results.
A few days later he came back to me and told me that he was able to get Excel to produce values in LINEST where the number of rows was less than the number of regressors. I really had a hard time believing this and because of the difference in time zones and language I started investigating on my own.
I use Google Sheets a lot more than I use Excel these days. I created a Sheet with 4 regressors plus the intercept but with only three rows of data:
