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);
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):
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
VB:
Var = Application.WorksheetFunction.LinEst(Sheets("references").Range("CP25:CP27"), Sheets("references").Range("CQ25:CQ27^{1,2}"), 1) [COLOR=#333333][/COLOR]
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).
I have a VBA function that calculates polynomial coefficients for a series of data pairs. One selects the range of cells that the coefficients are to be stored in, and enters the polynomial formula:
{POLFIT(Xa, Ya, N)}
Where Xa is the array of ordinate values, Ya is the array of data values, and N is the polynomial order to be fit.
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.
I am looking for a way to test whether enough cells were selected for the range formula: The function declaration is
Function POLFIT(Xa, Ya, N As Integer) As Variant
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