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#1
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I cannot display all the poly equation constants on the chart.
Using 2007: when openning up a 2000 spreadsheet, a chart that used to display
the equation for a 6th order poly only displays the the last 3 constants. I have looked at the trendline formating tools available and every thing is set correctly. The trendline is drawn correctly and changes, as you would expect, when I increase the poly order. |
#2
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I cannot display all the poly equation constants on the chart.
I've heard of issues with Excel 2007's display of the polynomial formula.
You could get the values in the worksheet using LINEST, as Bernard explains: http://people.stfx.ca/bliengme/ExcelTips/Polynomial.htm Keep in mind that a sixth order fit is generally not physically meaningful, but may only serve to make the line look nice. Depending on the data you are plotting, you may find it more sensible to use a relationship that matches a theoretical model. - Jon ------- Jon Peltier, Microsoft Excel MVP Tutorials and Custom Solutions Peltier Technical Services, Inc. - http://PeltierTech.com _______ "daz" wrote in message ... Using 2007: when openning up a 2000 spreadsheet, a chart that used to display the equation for a 6th order poly only displays the the last 3 constants. I have looked at the trendline formating tools available and every thing is set correctly. The trendline is drawn correctly and changes, as you would expect, when I increase the poly order. |
#3
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I cannot display all the poly equation constants on the chart.
Thanks for your reply Jon,
I was going to add that I'm already using the linest function for the the number crunching. However, why mess up a good feature. In 2000 I could copy and paste the contants quickly into a cell to generate a comparison with the raw data. Will this be fixed or explained? I have read a few comments about the six order poly should only be used for making things pretty. I have to disagree. If the number is set to scientific and 8 sig figs are used, a trendline can replicate raw data points very accurately. I generate calibration curves for venturi nozzles from NEL empirical data using excel 2000. The coefficients generated are identical to other software analysis tools I use for programming. regards Daz "Jon Peltier" wrote: I've heard of issues with Excel 2007's display of the polynomial formula. You could get the values in the worksheet using LINEST, as Bernard explains: http://people.stfx.ca/bliengme/ExcelTips/Polynomial.htm Keep in mind that a sixth order fit is generally not physically meaningful, but may only serve to make the line look nice. Depending on the data you are plotting, you may find it more sensible to use a relationship that matches a theoretical model. - Jon ------- Jon Peltier, Microsoft Excel MVP Tutorials and Custom Solutions Peltier Technical Services, Inc. - http://PeltierTech.com _______ "daz" wrote in message ... Using 2007: when openning up a 2000 spreadsheet, a chart that used to display the equation for a 6th order poly only displays the the last 3 constants. I have looked at the trendline formating tools available and every thing is set correctly. The trendline is drawn correctly and changes, as you would expect, when I increase the poly order. |
#4
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I cannot display all the poly equation constants on the chart.
The point about 6th order fits is not that Excel's differ from those
calculated by other packages, but that these fits are not based on any models of physical behavior, but rather on conforming "nicely" to the measured points. If you are interpolating by using the fit, you will get reasonable predictions. If you extrapolate too far beyond the range of observations, you could be very far from the true behavior. - Jon ------- Jon Peltier, Microsoft Excel MVP Tutorials and Custom Solutions Peltier Technical Services, Inc. - http://PeltierTech.com _______ "daz" wrote in message ... Thanks for your reply Jon, I was going to add that I'm already using the linest function for the the number crunching. However, why mess up a good feature. In 2000 I could copy and paste the contants quickly into a cell to generate a comparison with the raw data. Will this be fixed or explained? I have read a few comments about the six order poly should only be used for making things pretty. I have to disagree. If the number is set to scientific and 8 sig figs are used, a trendline can replicate raw data points very accurately. I generate calibration curves for venturi nozzles from NEL empirical data using excel 2000. The coefficients generated are identical to other software analysis tools I use for programming. regards Daz "Jon Peltier" wrote: I've heard of issues with Excel 2007's display of the polynomial formula. You could get the values in the worksheet using LINEST, as Bernard explains: http://people.stfx.ca/bliengme/ExcelTips/Polynomial.htm Keep in mind that a sixth order fit is generally not physically meaningful, but may only serve to make the line look nice. Depending on the data you are plotting, you may find it more sensible to use a relationship that matches a theoretical model. - Jon ------- Jon Peltier, Microsoft Excel MVP Tutorials and Custom Solutions Peltier Technical Services, Inc. - http://PeltierTech.com _______ "daz" wrote in message ... Using 2007: when openning up a 2000 spreadsheet, a chart that used to display the equation for a 6th order poly only displays the the last 3 constants. I have looked at the trendline formating tools available and every thing is set correctly. The trendline is drawn correctly and changes, as you would expect, when I increase the poly order. |
#5
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I cannot display all the poly equation constants on the chart.
On Oct 17, 3:08 pm, "Jon Peltier"
wrote: The point about 6th order fits is not that Excel's differ from those calculated by other packages, Although for some difficult problems they do! Historically in old XL versions the polynomial fit used inside the old graph charting software had significantly better numerical stability than LINEST. And I honestly would not trust LINEST with anything beyond a cubic polynomial in any version of Excel. I have seen it fail too often. but that these fits are not based on any models of physical behavior, but rather on conforming "nicely" to the measured points. If you are interpolating by using the fit, you will get reasonable predictions. If you extrapolate too far beyond the range of observations, you could be very far from the true behavior. It also depends how many measured points you have and their distribution. If there are too few points then you can get an excellent least squares fit *at the specified data points* and wild oscilations inbetween. "daz" wrote in message ... Thanks for your reply Jon, I was going to add that I'm already using the linest function for the the number crunching. However, why mess up a good feature. In 2000 I could copy and paste the contants quickly into a cell to generate a comparison with the raw data. Will this be fixed or explained? I have read a few comments about the six order poly should only be used for making things pretty. I have to disagree. If the number is set to scientific and 8 sig figs are used, a trendline can replicate raw data points very accurately. I generate calibration curves for venturi nozzles from NEL empirical data using excel 2000. The coefficients generated are identical to other software analysis tools I use for programming. It depends very much on what you are doing. Usually it is better to use a physical model of the problem in hand rather than fitting a generic high order polynomial. In some circumstance you know on purely physical grounds that the calibration should for example contain only odd or even powers of the dependent variable. Regards, Martin Brown |
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