Calculate y-value from chart

[perolav]

Hi,
I have a set of data, 100 x-values with corresponding y-values. Onl
about every third of the y's have a value, but by letting exce
interpolate the graph, I can see how the graph should look like.

My questions are:
1. Can excel give me the formula to the graph it has drawn? Somethin
like: "Show Equation"?

2. Is there a way to find out the y-value to a corresponding x-value
The graph has no standard-form, ie. it's not a parabel, so I don't kno
if I can use "trend" or "forecast"? The form of the graph is highl
irregular, but excel managed to draw the graph, so it must know al
it's y-values?

Please ask if anything is badly explained.

Thanks, perola

 

[Bernard Liengme]

We would need to see the data to answer this - if the curve is smooth I
expect a trendline can be found.
Send me file - my email not the group

 

[Tushar Mehta]

AFAIK, MS has never published its smoothened curve algorithm. The
closest anyone has come to figuring it out is Brian Murphy with his
Bezier curve approximation. See the downloadable file at
http://xlrotor.com/resources/files.shtml

Dave Braden's cubic spline algorithm also comes close. Search the
google.com archive of the XL newsgroups.

--
Regards,

Tushar Mehta
www.tushar-mehta.com
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