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Polynomial curve fitting with EXCELL

Polynomial curve fitting with EXCELL

Polynomial curve fitting with EXCELL

(OP)
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

RE: Polynomial curve fitting with EXCELL

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

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

RE: Polynomial curve fitting with EXCELL

(OP)

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

RE: Polynomial curve fitting with EXCELL

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?

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RE: Polynomial curve fitting with EXCELL

(OP)
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,...

RE: Polynomial curve fitting with EXCELL

"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.

RE: Polynomial curve fitting with EXCELL

(OP)
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,...

RE: Polynomial curve fitting with EXCELL

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.

RE: Polynomial curve fitting with EXCELL

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

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