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.
Obtaining a quadratic function igven three points on a curve
4 messages · Barth B. Riley, David Scott, Joshua Wiley
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 <bbriley at 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 at 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/
I think you need poly(X, 2, raw = TRUE) to interpret the coefficients
in the manner described below.
poly uses orthogonal polynomials by default:
poly package:stats R Documentation
Compute Orthogonal Polynomials
Description:
Returns or evaluates orthogonal polynomials of degree 1 to
'degree' over the specified set of points 'x'. These are all
orthogonal to the constant polynomial of degree 0. Alternatively,
evaluate raw polynomials.
David Scott
On 21/01/2011 3:50 a.m., Joshua Wiley wrote:
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<bbriley at 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 at 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.
_________________________________________________________________ David Scott Department of Statistics The University of Auckland, PB 92019 Auckland 1142, NEW ZEALAND Phone: +64 9 923 5055, or +64 9 373 7599 ext 85055 Email: d.scott at auckland.ac.nz, Fax: +64 9 373 7018 Director of Consulting, Department of Statistics
Many thanks for the correction David. Josh
On Thu, Jan 20, 2011 at 7:17 AM, David Scott <d.scott at auckland.ac.nz> wrote:
I think you need poly(X, 2, ?raw = TRUE) to interpret the coefficients in the manner described below. poly uses orthogonal polynomials by default: poly ? ? ? ? ? ? ? ? ? package:stats ? ? ? ? ? ? ? ? ? R Documentation Compute Orthogonal Polynomials Description: ? ? Returns or evaluates orthogonal polynomials of degree 1 to ? ? 'degree' over the specified set of points 'x'. These are all ? ? orthogonal to the constant polynomial of degree 0. ?Alternatively, ? ? evaluate raw polynomials. David Scott
[snip]
--
_________________________________________________________________ David Scott ? ? Department of Statistics ? ? ? ? ? ? ? ?The University of Auckland, PB 92019 ? ? ? ? ? ? ? ?Auckland 1142, ? ?NEW ZEALAND Phone: +64 9 923 5055, or +64 9 373 7599 ext 85055 Email: ?d.scott at auckland.ac.nz, ?Fax: +64 9 373 7018 Director of Consulting, Department of Statistics