Polynomial curve fitting with EXCELL

[lvallieres44]

Hi,
With 2 columns (X and Y) of data, I got from Excell 2003 the curve and the following equation : y = 23E-04X3 + 4E-05X2 - 3E-06X + 0,007
What E means ? Is it Sigma symbol?
I am not familiar with this application.

How can I use this formula to get Y values from any X input ?

Thanks

 

[PEDARRIN2]

E-04 means 10 to the power of -4 or 0.0001.

So 23E-04 is 23 x 10^-4 or 0.0023.

 

[lvallieres44]

Hi,
From the two columns of data below, I got the formula: 6E-09X^3-3E-05X^2+0,0165X+6,3375 with R^2=1
However, when I enter one value coming from the data, let's say 1071, I get the wrong number of -3,03
It should be 2. Please, let me know how to match correctly the best fit curve.

CFM Static pressure Performance from fan curve:
(in) Cfm Static pressure
1127 1 1071 -3,03
1071 2
1014 3
953 4
888 5
817 6
736 7
638 8

 

[IRstuff]

Where did you get your "equation" from? Excel's polynomial trendline gives y = 5.9678E-09x3 - 2.5550E-05x2 + 1.6476E-02x + 6.3375E+00 (R² = 1.0000E+00)

Why do you think that a single digit of precision is adequate for this task? Is this a homework assignment?


TTFN
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[lvallieres44]

Hummm,

I got this equation from Excel's polynomial trendline.
I have no idea how to get more digit,...
These data are from a fan performance table. We try to get the equation of this fan curve
to be able to have performance at any point on the curve.
Must know how to get more digit,...

 

[IRstuff]

Format Trendline Label

TTFN
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[MintJulep]

"Best Fit" in no way means that the equation will return an exact match for any given coordinate pair.

It means that the equation describes the mathematical function that best describes ALL of the points.

 

[IRstuff]

But, in this case, the fit is very good. Largest error is the second point at 0.38% error.

TTFN
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[lvallieres44]

I am using EXCEL 2010, and I can't find the way to format Trenline Label to get more digit in the
polynomial equation,...
Excel give me only one digit,...

 

[IRstuff]

> Right click trendline label
> Select Format Trendline Label ( 3rd from bottom
> Select Number | Scientific | 4 digits


TTFN
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[MintJulep]

Use the LINEST() function to return the coefficients as useable values in the worksheet.

It's been discussed here in the spreadsheet forum many times. Search works.

 

[ProcessHVAC]

lvallieres: would you mind sending me your email and real name to make sure we don't hire you after you finish school? Just kidding....good luck with homework..previous responses solve your problem