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

My questions a
1. Can excel give me the formula to the graph it has drawn? Something
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 know
if I can use "trend" or "forecast"? The form of the graph is highly
irregular, but excel managed to draw the graph, so it must know all
it's y-values?

Please ask if anything is badly explained.

Thanks, perolav


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perolav
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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
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Bernard V Liengme
www.stfx.ca/people/bliengme
remove caps from email

"perolav" wrote in
message ...

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

My questions a
1. Can excel give me the formula to the graph it has drawn? Something
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 know
if I can use "trend" or "forecast"? The form of the graph is highly
irregular, but excel managed to draw the graph, so it must know all
it's y-values?

Please ask if anything is badly explained.

Thanks, perolav


--
perolav
------------------------------------------------------------------------
perolav's Profile:
http://www.excelforum.com/member.php...o&userid=26163
View this thread: http://www.excelforum.com/showthread...hreadid=394854

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

In article ,
says...

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

My questions a
1. Can excel give me the formula to the graph it has drawn? Something
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 know
if I can use "trend" or "forecast"? The form of the graph is highly
irregular, but excel managed to draw the graph, so it must know all
it's y-values?

Please ask if anything is badly explained.

Thanks, perolav


--
perolav
------------------------------------------------------------------------
perolav's Profile: http://www.excelforum.com/member.php...o&userid=26163
View this thread: http://www.excelforum.com/showthread...hreadid=394854