Calculate y-value from chart

  • Thread starter Thread starter perolav
  • Start date Start date
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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
 
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
 
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
Excel, PowerPoint, and VBA add-ins, tutorials
Custom MS Office productivity solutions
 
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