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Curve-Fitting in Excel

Curve-Fitting in Excel

(OP)
This may be asking for too much, but is there a way to start out with a "template" formula such as

X =ay^4+by^3+cy^2+dy^n+e (where n<2) or, if necessary, it could be simpler such as X=ay^3+by^2+cy^n+d

Then listing all of the known data point x1,x2... and y1,y2... etc

And then being able to solve for the general equation "template"

I say template because the curve may be closer to a logarithmic function, but a polynomial such as the template would be close enough.

(Ithas been decades since I have beenin University and my math skills have become very rusty)

RE: Curve-Fitting in Excel

Does the LOGEST() function do what you are trying to do?

Note that it as an ARRAY function.

RE: Curve-Fitting in Excel

(OP)
Sorry, what I meant:

The curve could be either be logarithmic or not. I don't need lot of accuracy, so if it is logarithmic, could it be expressed as that "template" polynomial within reasonable accuracy?

RE: Curve-Fitting in Excel

(OP)
cowski, thanks, that link looks useful.

RE: Curve-Fitting in Excel

(OP)
I wanted to make it easier by downloading the free CurveExpert version, but there seems to be a Windows 64 bit vs 32 bit problem.

RE: Curve-Fitting in Excel

I'm still not clear on what you are trying to accomplish?

Are you looking for what equation will give you the "prettiest" fit?

Plot your points and use the "Add Trendline" feature. Try the various types until you get a curve that has enough reasonable accuracy for you. Toggle on "Show Equation" to grab the coefficients.

RE: Curve-Fitting in Excel

(OP)
@MintJulep

I am looking for what you are assuming - trying to determine the coefficients and trying to see if it is a Y^3 or else a y^2 function.

I haven't used any of the Excel curve fitting functions yet and I was trying to arrive at the easy dumbed-down solution because I am too rusty with math.

RE: Curve-Fitting in Excel

Quote (Aellc)

I was trying to arrive at the easy dumbed-down solution because I am too rusty with math.

You and me both.

My earlier solution is what you want to play with then.

Plot your points and use the "Add Trendline" feature. Try the various types until you get a curve that has enough reasonable accuracy for you. Toggle on "Show Equation" to grab the coefficients.

Point and click. No math required.

RE: Curve-Fitting in Excel

(OP)
Thanks Doug

That really makes it easy for me.

RE: Curve-Fitting in Excel

(OP)
I am finding that once it gives me a solution, I can go in and tweak coefficients and adjust powers (i.e. ^2.2 instead of ^2) to get the resulting formula spot-on.

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