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#1
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How can I curve fit in Excel?
I am trying to determine the equation defining a curve in Excel. When I
apply a trendline using a polynomial equation, the equation returned is incorrect. Is there a method to "fit a curve" and determine the equation defining the curve? |
#2
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How can I curve fit in Excel?
Why do you think it incorrect. My bet is you have too few decimals
displayed. Format the trendline equation to show 15 places and try again. Then experiment with LINEST to get polynomial coefficients as shown at http://www.stfx.ca/people/bliengme/E...Polynomial.htm best wishes -- Bernard V Liengme www.stfx.ca/people/bliengme remove caps from email "Jimg" wrote in message ... I am trying to determine the equation defining a curve in Excel. When I apply a trendline using a polynomial equation, the equation returned is incorrect. Is there a method to "fit a curve" and determine the equation defining the curve? |
#3
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How can I curve fit in Excel?
The other common user error is to use a "Line" chart instead of an "XY
(Scatter) chart. This will result in coefficients that are actually wrong, instead of merely rounded beyond usefulness. The "Line" chart occurs earlier in the chart-type menu and is misleadingly named, inviting the obvious (but wrong) interpretation that it has something to do with whether you want to connect the points by a line. A "Line" chart is a chart where the x-axis is composed of categories instead of a numeric scale (unclear how MS got "Line" out of that). If you provide x-axis information at all, then it is interpreted as category labels, even if the range solely contains numeric values. If you request a trendline (unclear why MS supports trends on non-numeric x-values), then the x-values for the trend are taken to be 1,2,3,... regardless of the actual x-data provided. Jerry "Bernard Liengme" wrote: Why do you think it incorrect. My bet is you have too few decimals displayed. Format the trendline equation to show 15 places and try again. Then experiment with LINEST to get polynomial coefficients as shown at http://www.stfx.ca/people/bliengme/E...Polynomial.htm best wishes -- Bernard V Liengme www.stfx.ca/people/bliengme remove caps from email "Jimg" wrote in message ... I am trying to determine the equation defining a curve in Excel. When I apply a trendline using a polynomial equation, the equation returned is incorrect. Is there a method to "fit a curve" and determine the equation defining the curve? |
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