Hi Barth,
Here is an option fitting a linear model toa second order polynomial
and extracting the coefficients. The Intercept corresponds to "c" in
your email, then poly(...)1 to "b" and poly(...)2 to "a".
################
dat <- read.table(textConnection("
Y X
0.159529 0
0.5 0.773019
1 1"), header = TRUE)
closeAllConnections()
coef(lm(Y ~ poly(X, 2), data = dat))
#################
For details see:
?poly
?lm
?coef
Hope this helps,
Josh
On Thu, Jan 20, 2011 at 6:42 AM, Barth B. Riley <bbri...@chestnut.org> wrote:
> Hello
>
> I would like to obtain the coefficients for a quadratic function (ax^2 + bx +
> c) given three sets of points on the quadratic curve. For instance:
>
> Y X
> 0.159529 0
> 0.5 0.773019
> 1 1
>
> Is there a function in R to obtain the a, b and c ceofficients?
>
> Thanks
>
> Barth
>
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--
Joshua Wiley
Ph.D. Student, Health Psychology
University of California, Los Angeles
http://www.joshuawiley.com/
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