[R] sinusoidal relationship

[Ravi Varadhan]

I assume that you are trying to fit the sinusoidal model, with an error
term, to data:

	y = a * sin(b*x) + error

Here you can use the `nls' function for non-linear least-squares.  

?nls

Here is an example:

a <- 0.5

b <- 0.2

x <- seq(0, 10, length=100)

eps <- rnorm(length(x), sd=0.1)

y <- a*sin(b*x) + eps 

plot(x, y, type="p")

nls(y ~ a * sin(b*x), start=list(a=0.1, b=0.1))


Note that `nls' will fail to converge without the "error" term.

Best,
Ravi.  

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Ravi Varadhan, Ph.D.

Assistant Professor, The Center on Aging and Health

Division of Geriatric Medicine and Gerontology 

Johns Hopkins University

Ph: (410) 502-2619

Fax: (410) 614-9625

Email: rvaradhan at jhmi.edu

Webpage:
http://www.jhsph.edu/agingandhealth/People/Faculty_personal_pages/Varadhan.h
tml

 

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-----Original Message-----
From: r-help-bounces at r-project.org [mailto:r-help-bounces at r-project.org] On
Behalf Of HAKAN DEMIRTAS
Sent: Wednesday, October 07, 2009 11:28 AM
To: r-help at r-project.org
Subject: [R] sinusoidal relationship

Hi,

Suppose x and y are vectors whose elements are known. I know that there is a
sinusoidal relation between them. In other words,
y=a*sin(bx) where b is probably a function of pi. 

How do I find a and b in R?

Hakan
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