Finding an equation for a curve in Excel?
Finding an equation for a curve in Excel?
(OP)
Hi,
I have some data points that form a curve.
I wish to put the points into excel and get it to put an equation to the line.
Do you know what is th name of the Excel math software feature that does this...so that i can install it.
Also, do you know how i can go about this?
I have some data points that form a curve.
I wish to put the points into excel and get it to put an equation to the line.
Do you know what is th name of the Excel math software feature that does this...so that i can install it.
Also, do you know how i can go about this?





RE: Finding an equation for a curve in Excel?
http://www.cadreanalytic.com/Regress.htm
it is free and is better than Excel.
Onda
RE: Finding an equation for a curve in Excel?
If you just want the coefficients you can use the LINEST() or LOGEST() functions. They are array functions, so read help carefully.
RE: Finding an equation for a curve in Excel?
Tata but not yet tara
RE: Finding an equation for a curve in Excel?
w tried excel and cadreanalytic and bith didn't work when we selected cubic polynomial.
Excel showed us a graph that was a near perfect fit............it also gave us the equation....but when we plotted it ourselves it did not agree with the excel function.
-do you know what we can do?
(our data points were almost a straight line but with a bit of a wiggle , so we tried cubic.)
RE: Finding an equation for a curve in Excel?
I don't know why regress don't work for you.
I've used a lot with always good result.
RE: Finding an equation for a curve in Excel?
TTFN
FAQ731-376: Eng-Tips.com Forum Policies
Chinese prisoner wins Nobel Peace Prize
RE: Finding an equation for a curve in Excel?
Tata but not yet tara
RE: Finding an equation for a curve in Excel?
thanks
RE: Finding an equation for a curve in Excel?
thanks anyway.
RE: Finding an equation for a curve in Excel?
=LINEST(yvalues, xvalues^COLUMN($A:$C))
I prefer:
=LINEST(yvalues, xvalues^{1,2,3}) (note curly brackets)
but they give the same answer, and the same as the trend line in a chart for the same data.
To get all 4 coefficients enter the formula as shown, select the cell with the formula and the adjacent three cells to the right, press F2, then ctrl-shift-enter.
You can also use the INDEX() function to return a coefficient other than the first one as a single value. e.g.:
=INDEX(LINEST(yvalues,xvalues^{1,2,3}),2)
to return the coefficient for x^2
Doug Jenkins
Interactive Design Services
http://newtonexcelbach.wordpress.com/
RE: Finding an equation for a curve in Excel?
These are the Excel graphs.....
http://i51.tinypic.com/1y0ht0.jpg
....thin black line = from our data.
....thick black line is what excel plotted
....pink line is our plot of the equation that excel
claims represents the thick black line
(as you can see, the thick black line and pink lines don't match.)
Our data is as follows......
X Y
820 1036
755 904
715 851
696 818
644 748
501 528
370 370
RE: Finding an equation for a curve in Excel?
we did the decimal place thing on the formula and its ok now.
thankyou to all.
RE: Finding an equation for a curve in Excel?
It's just a problem of digits!!
Regards
RE: Finding an equation for a curve in Excel?
Doug Jenkins
Interactive Design Services
http://newtonexcelbach.wordpress.com/
RE: Finding an equation for a curve in Excel?
a = -2.18445071972E+003
b = -2.55488142333E+003
Tata but not yet tara
RE: Finding an equation for a curve in Excel?
http://www