## 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)

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

Note that it as an ARRAY function.

## RE: Curve-Fitting in Excel

thread770-184726: Excel Curve Fit Coefficients

http://www.ithaca.edu/tpfaff/pdf/CurveFittingWithE...

## RE: Curve-Fitting in Excel

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

## RE: Curve-Fitting in Excel

## RE: Curve-Fitting in Excel

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

## RE: Curve-Fitting in Excel

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

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

Have a look at:

http://newtonexcelbach.wordpress.com/2011/01/19/us...

for ways of getting the information onto the spreadsheet, so it can be used in other calculations.

Doug Jenkins

Interactive Design Services

http://newtonexcelbach.wordpress.com/

## RE: Curve-Fitting in Excel

That really makes it easy for me.

## RE: Curve-Fitting in Excel