excel generated polynomial equation is wrong jkeith 26.09.2006 18:44:02 fitting a trendline to data and the polynomial equation it spits out is obviously wrong. Any ideas? thanks

Re: excel generated polynomial equation is wrong "Bernard Liengme" <bliengme[ at ]stfx.TRUENORTH.ca> 26.09.2006 19:11:50 It is 'wrong' because the value of y=ax^4+bx^3+cx^2+dx+e if very sensitive to the values of the confinements (a, b,....) You could format the trendline and get more precision and then very carefully copy the values OR you could you LINEST as shown at http://people.stfx.ca/bliengme/ExcelTips/Polynomial.htm best wishes -- Bernard V Liengme www.stfx.ca/people/bliengme remove caps from email "jkeith" <jkeith[ at ]discussions.microsoft.com> wrote in message news:B93B8CCE-4C18-4C40-9B3B-17A06E14089B[ at ]microsoft.com... [Quoted Text] > fitting a trendline to data and the polynomial equation it spits out is > obviously wrong. Any ideas? thanks

Re: excel generated polynomial equation is wrong jkeith 26.09.2006 19:36:02 I understand what you are saying and fully agree, but that is not the issue. The equation is just flat wrong UNLESS you set the intercept =0. But doing that makes the line not fit as well. Any thoughts? Thanks for your time. "Bernard Liengme" wrote: [Quoted Text] > It is 'wrong' because the value of y=ax^4+bx^3+cx^2+dx+e if very sensitive > to the values of the confinements (a, b,....) > You could format the trendline and get more precision and then very > carefully copy the values OR you could you LINEST as shown at > http://people.stfx.ca/bliengme/ExcelTips/Polynomial.htm > best wishes > -- > Bernard V Liengme > www.stfx.ca/people/bliengme > remove caps from email > > "jkeith" <jkeith[ at ]discussions.microsoft.com> wrote in message > news:B93B8CCE-4C18-4C40-9B3B-17A06E14089B[ at ]microsoft.com... > > fitting a trendline to data and the polynomial equation it spits out is > > obviously wrong. Any ideas? thanks > > >

Re: excel generated polynomial equation is wrong jkeith 26.09.2006 19:51:02 I apologize- I was wrong- I took every number out to SIX decimal places and calculated...my answer went from 241 to 94.4 (correct). A bunch of engineers and we did not think it would make that kind of difference. Thanks for the help "jkeith" wrote: [Quoted Text] > I understand what you are saying and fully agree, but that is not the issue. > The equation is just flat wrong UNLESS you set the intercept =0. But doing > that makes the line not fit as well. Any thoughts? Thanks for your time. > > "Bernard Liengme" wrote: > > > It is 'wrong' because the value of y=ax^4+bx^3+cx^2+dx+e if very sensitive > > to the values of the confinements (a, b,....) > > You could format the trendline and get more precision and then very > > carefully copy the values OR you could you LINEST as shown at > > http://people.stfx.ca/bliengme/ExcelTips/Polynomial.htm > > best wishes > > -- > > Bernard V Liengme > > www.stfx.ca/people/bliengme > > remove caps from email > > > > "jkeith" <jkeith[ at ]discussions.microsoft.com> wrote in message > > news:B93B8CCE-4C18-4C40-9B3B-17A06E14089B[ at ]microsoft.com... > > > fitting a trendline to data and the polynomial equation it spits out is > > > obviously wrong. Any ideas? thanks > > > > > >

Re: excel generated polynomial equation is wrong "Bernard Liengme" <bliengme[ at ]stfx.TRUENORTH.ca> 26.09.2006 19:52:12 Send me (my private email) a sample file with the data. best wishes -- Bernard V Liengme www.stfx.ca/people/bliengme remove caps from email "jkeith" <jkeith[ at ]discussions.microsoft.com> wrote in message news:2B825BD2-C732-453D-9840-EDEAE1629557[ at ]microsoft.com... [Quoted Text] >I understand what you are saying and fully agree, but that is not the >issue. > The equation is just flat wrong UNLESS you set the intercept =0. But doing > that makes the line not fit as well. Any thoughts? Thanks for your time. > > "Bernard Liengme" wrote: > >> It is 'wrong' because the value of y=ax^4+bx^3+cx^2+dx+e if very >> sensitive >> to the values of the confinements (a, b,....) >> You could format the trendline and get more precision and then very >> carefully copy the values OR you could you LINEST as shown at >> http://people.stfx.ca/bliengme/ExcelTips/Polynomial.htm >> best wishes >> -- >> Bernard V Liengme >> www.stfx.ca/people/bliengme >> remove caps from email >> >> "jkeith" <jkeith[ at ]discussions.microsoft.com> wrote in message >> news:B93B8CCE-4C18-4C40-9B3B-17A06E14089B[ at ]microsoft.com... >> > fitting a trendline to data and the polynomial equation it spits out is >> > obviously wrong. Any ideas? thanks >> >> >>

Re: excel generated polynomial equation is wrong "Dana DeLouis" <ddelouis[ at ]bellsouth.net> 26.09.2006 20:33:56 [Quoted Text] > I took every number out to SIX decimal places and Hi. It's a known "feature." Chart trendline formula is inaccurate in Excel http://support.microsoft.com/kb/211967/en-us -- HTH :>) Dana DeLouis Windows XP & Office 2003 "jkeith" <jkeith[ at ]discussions.microsoft.com> wrote in message news:81722169-82FB-4F49-A254-A6E96266DF27[ at ]microsoft.com... >I apologize- I was wrong- I took every number out to SIX decimal places and > calculated...my answer went from 241 to 94.4 (correct). A bunch of > engineers > and we did not think it would make that kind of difference. Thanks for > the > help > > "jkeith" wrote: > >> I understand what you are saying and fully agree, but that is not the >> issue. >> The equation is just flat wrong UNLESS you set the intercept =0. But >> doing >> that makes the line not fit as well. Any thoughts? Thanks for your >> time. >> >> "Bernard Liengme" wrote: >> >> > It is 'wrong' because the value of y=ax^4+bx^3+cx^2+dx+e if very >> > sensitive >> > to the values of the confinements (a, b,....) >> > You could format the trendline and get more precision and then very >> > carefully copy the values OR you could you LINEST as shown at >> > http://people.stfx.ca/bliengme/ExcelTips/Polynomial.htm >> > best wishes >> > -- >> > Bernard V Liengme >> > www.stfx.ca/people/bliengme >> > remove caps from email >> > >> > "jkeith" <jkeith[ at ]discussions.microsoft.com> wrote in message >> > news:B93B8CCE-4C18-4C40-9B3B-17A06E14089B[ at ]microsoft.com... >> > > fitting a trendline to data and the polynomial equation it spits out >> > > is >> > > obviously wrong. Any ideas? thanks >> > >> > >> >

Re: excel generated polynomial equation is wrong "MartinW" <mtmw[ at ]hotmail.invalid> 26.09.2006 23:42:22 Hi Dana, The article you linked to says to set your number to 30 decimal places yet Excel will only display precision to 15 significant digits. Is this a situation where Excel will calculate to a higher precision but only display to the limits? Is it sort of like a cell only displaying 1024 characters even though it will accept and use a greater amount of data? Also, if that is the case, what is the limit of decimals. Thanks Martin

Re: excel generated polynomial equation is wrong "James Silverton" <not.jim.silverton[ at ]comcast.not> 27.09.2006 00:14:48 Hello, MartinW! You wrote on Wed, 27 Sep 2006 09:42:22 +1000: M> The article you linked to says to set your number to 30 M> decimal places yet Excel will only display precision to 15 M> significant digits. M> Is this a situation where Excel will calculate to a higher M> precision but only display to the limits? M> Is it sort of like a cell only displaying 1024 characters M> even though it will accept and use a greater amount of data? M> Also, if that is the case, what is the limit of decimals. From HELP on precision. 15 digit precision Excel stores and calculates with 15 significant digits of precision. Excel calculates stored, not displayed, values The displayed, and printed, value depends on how you choose to format and display the stored value. James Silverton Potomac, Maryland E-mail, with obvious alterations: not.jim.silverton.at.comcast.not

Re: excel generated polynomial equation is wrong "Dana DeLouis" <ddelouis[ at ]bellsouth.net> 27.09.2006 01:07:46 Hi. I think the 30 digits is to allow one to see all the digits using the basic Number format. If you format a cell with the Number format, and use the scroll button, you are limited to 30 digits. I think this is what the article was referring to. For example, if you enter the following number: =123456789012345*(1E-30) and use the number format out to 30 digits, you will be able to see all the digits. (Under Number format). So again, the article seems to suggest using the Number Format, and the Number format seems limited to 30 Digits. (as seen from the scroll buttons). What's funny is that the toolbar button "Increase Decimal" can override this limitation. -- HTH :>) Dana DeLouis Windows XP & Office 2003 "MartinW" <mtmw[ at ]hotmail.invalid> wrote in message news:OryOqVc4GHA.3452[ at ]TK2MSFTNGP05.phx.gbl... [Quoted Text] > Hi Dana, > > The article you linked to says to set your number to 30 decimal > places yet Excel will only display precision to 15 significant digits. > > Is this a situation where Excel will calculate to a higher precision > but only display to the limits? > Is it sort of like a cell only displaying 1024 characters even though > it will accept and use a greater amount of data? > Also, if that is the case, what is the limit of decimals. > > Thanks > Martin >

Re: excel generated polynomial equation is wrong "MartinW" <mtmw[ at ]hotmail.invalid> 27.09.2006 01:45:51 Thanks Dana and James, It was just curiosity on my part. 15 digits provides a lot more precision than I will ever need. Regards Martin