Dr Liegme;

Thanks for your quick reply.

I had previously extended the example from your website from a 3rd
order poly to a 6th order, no problem. At least it returned values for
all for all the cells. Unfortunately, the coefficients don't make
sense. When I try to re-create the curve using those values, the curve
does not match.

I would expect that the results be fairly similar to that shown by
Excel in the "display equation" option, however they are obviously
different.

I've tried to re-create your 3rd order polynomial example exactly as
you have displayed it on your webpage, but without success. Instead of
the coefficients,

{2,3,-6,8}

I get;

{2.16667, 2, 148.8333, -152.333}.

Clearly, I am having the same issue with the higher order polynomials.
As far as I can tell, I am recreating your example and the LINEST
function exactly as you have shown and I can't explain the difference
between your results and mine. I will go back and try to trouble-shoot
the 3rd order poly example to get your results. Any insight you have
would again be appreciated.

Thanks
Kevin

PS. I am using a 6th order polynomial to describe a curve that I have
digitized. I have ~1000 x-y data points. I would like to have the
equation so that I can input a given x value (in my case stress) and
return a given y value (in my case, the Larson-Miller Parameter). I
don't plan to extrapolate as I understand that high order polynomials
tend to rapidly diverge. Indeed, when I use excel's trendline function
to extend the chart, it is okay on one end of the curve, but 'curls
over' on the other end.


--
KevinW
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