Extracting Variables From Quartic Function (4th Degree Polynomial)

Apr 10, 2012

I have quite a number of 4th degree polynomials and attempting to extract the variables from every equation. I used the formula below (from another thread);

=LOOKUP(99^99,--("0"&MID(A1,MIN(SEARCH({0,1,2,3,4,5,6,7,8,9},A1&"0 123456789")),ROW($1:$10000))))

but it only extracts the first variable.

4th degree polynomial function: f(x) = ax^4 + bx^3 + cx^2 + dx + e

Example of one of the equations: Y = -42.4276 + 319.989 X - 809.094 X^2 + 942.247 X ^3 - 397.587 X^4

I'll like to have the final result like below (Based on the Example equation above)


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Jul 31, 2008

I have this data:

x y
310 516
320 526
325 535
330 587
335 640
340 715
345 857
350 1040

When I perform a third degree polynomial curve fit I get this equation:
y = 0.0106x3 - 10.0266x2 + 3152.3381x - 329943.8370
R2 = 0.9987

Which isnt right. On a calculator, I get negative numbers. Does excel have problems with 3rd degree polynomials?

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i have a function in a cell (that works) to extract coefficients from a range of cells in a workbook:

VB: =INDEX(LINEST(CP25:CP27,CQ25:CQ27^{1,2}),1)}

i have variables for cp25:cp27 and cq25:cq27 already defined in my vba code. the values for these in the case i am working on are as follows (returns 110.5):

cp25 = 560
cp26 = 570
cp27 = 580
cq25 = .414
cq26 = .479
cq27 = .536

1) how to do this function in VBA only - this is part of a UDF and cannot have any helper cells
2) how to refer to 560,570,580 as a 'range'. is there a way to put these six variables into my ranges for later processing?

All of the google searches i have deal only with linear regression, taking from existing graphs, or say to just use the function i have above.

I have tried


Var = Application.WorksheetFunction.LinEst(Sheets("references").Range("CP25:CP27"), Sheets("references").Range("CQ25:CQ27^{1,2}"), 1)

but return #value! errors. when i remove the ^{1,2} portion, i do return a value but it is incorrect (returns 160), what is the correct syntax for adding in the ^{1,2}? if you do that would be fantastic, but brings me back to issue #2 in that i need to refer to my variables in the vba code and not this range (as they will eventually be going away).

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Feb 9, 2010

I have plotted a graph which compares the miles done with the petrol used.

I'm trying find a formula which allows me to apply the petrol and would give me the miles covered.

From excel I have applied the tread line of polynomial and obtained the following formula...

y = 1E-06x5 - 0.0002x4 + 0.0161x3 - 0.4893x2 + 7.5295x - 20.87

Rē = 0.9989

When is it applied to excel with the value of petrol it does not give me the miles.
I'm working out the formula in a incorrect manner?

I have attached the excel file.

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It is obvious that one needs to select at least N+1 cells when the array funtion is typed in. But, it is easy to select too few cells.

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Tp std


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I've been stubbornly struggling with this on and off for a couple of weeks now and I'm not getting any closer to working it out and the websites I've found explaining the procedure all seem to go over my head by the time I get into the fourth or fifth paragraph.

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