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 > > PRIVILEGED AND CONFIDENTIAL INFORMATION > This transmittal and any attachments may contain PRIVILEGED AND > CONFIDENTIAL information and is intended only for the use of the > addressee. If you are not the designated recipient, or an employee > or agent authorized to deliver such transmittals to the designated > recipient, you are hereby notified that any dissemination, > copying or publication of this transmittal is strictly prohibited. If > you have received this transmittal in error, please notify us > immediately by replying to the sender and delete this copy from your > system. You may also call us at (309) 827-6026 for assistance. > > ______________________________________________ > R-help@r-project.org mailing list > https://stat.ethz.ch/mailman/listinfo/r-help > PLEASE do read the posting guide http://www.R-project.org/posting-guide.html > and provide commented, minimal, self-contained, reproducible code. > -- Joshua Wiley Ph.D. Student, Health Psychology University of California, Los Angeles http://www.joshuawiley.com/ ______________________________________________ R-help@r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code.