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Polynomial least squares fit
Hi,
I have a graph of two values and I need to know, what the formula is that connects all to points. The trend function in the graph gives y = 0.0557x4 - 51.355x3 + 18559x2 - 3E+06x + 2E+08 I need the last two terms too more places. Is there a spread sheet function for this, a macro or anything. MarkS |
#2
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Polynomial least squares fit
On Mon, 18 Aug 2003 00:32:03 -0700, "Mark Scholes"
wrote: Hi, I have a graph of two values and I need to know, what the formula is that connects all to points. The trend function in the graph gives y = 0.0557x4 - 51.355x3 + 18559x2 - 3E+06x + 2E+08 I need the last two terms too more places. Is there a spread sheet function for this, a macro or anything. MarkS Select the equation on the chart. Then right-click and select Format Data Labels. The Number tab allows formatting the numbers in the equation to more decimal places (although Excel's precision limits makes formatting to more than 15 places meaningless). You can also use the LINEST worksheet function if the above is not satisfactory. The LINEST function does not always return the right answer, although it works pretty well most of the time. The algorithms used in the chart trendline generator is more robust. For my limited uses, LINEST has been satisfactory. If you search the archives using GOOGLE you will find techniques for not only using LINEST, but for also extracting the equation from the chart. --ron |
#3
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Polynomial least squares fit
David Braden's has VBA code to extract the coefficients directly from
the chart into cells is given at http://groups.google.com/groups?selm....microsoft.com LINEST does work well with non-challenging data, the problem is that it gives no warning when it fails completely. Jery Ron Rosenfeld wrote: On Mon, 18 Aug 2003 00:32:03 -0700, "Mark Scholes" wrote: Hi, I have a graph of two values and I need to know, what the formula is that connects all to points. The trend function in the graph gives y = 0.0557x4 - 51.355x3 + 18559x2 - 3E+06x + 2E+08 I need the last two terms too more places. Is there a spread sheet function for this, a macro or anything. MarkS Select the equation on the chart. Then right-click and select Format Data Labels. The Number tab allows formatting the numbers in the equation to more decimal places (although Excel's precision limits makes formatting to more than 15 places meaningless). You can also use the LINEST worksheet function if the above is not satisfactory. The LINEST function does not always return the right answer, although it works pretty well most of the time. The algorithms used in the chart trendline generator is more robust. For my limited uses, LINEST has been satisfactory. If you search the archives using GOOGLE you will find techniques for not only using LINEST, but for also extracting the equation from the chart. --ron |
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