Thread: Calculate y-value from chart

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 are:
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

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" <perolav.1tlbir_1123747567.6874@excelforum-nospam.com> wrote in
message news:perolav.1tlbir_1123747567.6874@excelforum-nospam.com...
>
> 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 are:
> 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 <perolav.1tlbir_1123747567.6874@excelforum-nospam.com>,
perolav.1tlbir_1123747567.6874@excelforum-nospam.com 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 are:
> 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
>
>