Sorry for confusing you,

Here it is more-
Excell 2002,
I was comparing coefficients with extracting using LINEST function to the
constants of displayed trend eq (6th order) with full precission. They are
all different.

Thanks for your valuable information.
Sanjay Limbikai

"Jerry W. Lewis" wrote:

You have given far too little information for us to be able to
accurately diagnose.

What version of Excel?
How are you fitting the polynomial? (chart trendline equation, LINEST,
other?)
What unexpected results are you getting?
Is the data set small enough that you could reasonably include it in
your post? (body text, no attachments, please)

While it is quite likely that you are over-fitting the data (as Tushar
suggested), it is not clear how that, in and of itself, would produce
"unexpected results". If you are using LINEST in versions prior to
Excel 2003, you could easily be in terretory where LINEST's algorithm
has numerical difficulties (how do coefficient estimates compare with
the chart trendline coefficients? [which is much better numerically]).
LINEST in Excel 2003 is much better numerically than previous versions,
but coefficients that are exactly zero are not to be trusted (again, how
do they compare to the chart trendline coefficients?). If you are using
the chart trendline coefficients and copying them into a worksheet for
further calculation, did you obtain them to full precision (format the
chart equation element to scientific notation with 14 decimal places) or
did you copy the heavily rounded values that Excel displays by default?

Jerry

Sanjay Kumar Limbikai wrote:

Hi,

If I evaluate my 6th order poly equation in Excell, it yields unexpected
results, but the eq works well for 1 to 5th order polynomial trend chart.
is there another way to work with 6th order poly eq. Any help would be
highly appreciated.

Thanks
Sanjay Limbikai