Hello, Jerry!
You wrote on Mon, 14 Aug 2006 09:28:01 -0700:

JWL LINEST in 2003 introduced an algorithm that is far better
JWL numerically than earlier versions (essentially as good as
JWL the chart trendline). However there is a bug in the
JWL implementation of that algorithm that can produce one or
JWL more coefficients that are exactly zero when they should
JWL be far from zero, even though earlier versions would have
JWL experienced no numerical difficulties on these particular
JWL data
JWL setshttp://groups.google.com/group/microsoft.public.excel.
JWL programming/browse_frm/thread/aaa78a91ec42fd4b/98be08e90c3
JWL cfa#98be08e90c3cfa

JWL The publically available 2007 beta appears to have fixed
JWL the problem in the new LINEST algorithm.

JWL Bottom line: for most simple stuff it won't matter whether
you
JWL use LINEST or the chart trendline. However, for any
JWL version prior to 2003, if there is a discrepancy between
JWL the chart trendline and LINEST, then don't believe LINEST.
JWL (This assumes that you are using an "XY (Scatter)" chart
JWL with numeric x-data provided--otherwise the chart
JWL trendline may not mean what you expect it too.)
JWL Similarly, if LINEST in 2003 (PC) or 2004 (Mac) reports
JWL any coefficient as exactly zero, don't believe it without
JWL indepenent verification (such as the chart trendline).

JWL Jerry

JWL "James Silverton" wrote:

?? Hello, All!
??
?? I have read complaints about lack of agreement in the
?? coefficients of polynomials obtained by fitting trendlines
?? on the graph and those obtained from LINEST. I had
?? occasion to do some experiments yesterday using a third
?? order polynomial with Excel 2002 and, as far as I can
?? tell, at the same number of decimal places the coefficient
?? results are identical. The data used had random errors and
?? was not from an exact curve.
??
?? Can anyone tell me which versions of Excel can be relied
?? on or else what problems I should look out for?

Thanks very much! I had assumed that the trendline might be less
accurate than LINEST. Again, I live and learn!

James Silverton
Potomac, Maryland

E-mail, with obvious alterations:
not.jim.silverton.at.comcast.not