Hi George,
I tried the following and it worked for me,
btmp.bi <- function(par., vec){
p <- par.[1]
mu1 <- par.[2]
mu2 <- par.[3]
sigma1 <- par.[4]
sigma2 <- par.[5]
-sum(log( plogis(p)*dnorm(vec, mu1, abs(sigma1)) + (1-plogis(p))*dnorm(vec, mu2, abs(sigma2)) ))
}
vec <- ifelse(runif(500)<.4, rnorm(1, 38, 1), rnorm(1, 40, 1))
optim(par=c(p=0.4, mu1=38, mu2=40, sigma1=1, sigma2=1), btmp.bi, method="CG", vec=vec)
I hope it helps.
Best, Dimitris
---- Dimitris Rizopoulos Ph.D. Student Biostatistical Centre School of Public Health Catholic University of Leuven
Address: Kapucijnenvoer 35, Leuven, Belgium Tel: +32/16/396887 Fax: +32/16/337015 Web: http://www.med.kuleuven.ac.be/biostat/ http://www.student.kuleuven.ac.be/~m0390867/dimitris.htm
----- Original Message ----- From: "George W. Gilchrist" <[EMAIL PROTECTED]>
To: <[EMAIL PROTECTED]>
Sent: Thursday, September 16, 2004 4:59 PM
Subject: [R] Estimating parameters for a bimodal distribution
For several years, I have been using Splus to analyze an ongoing series of
datasets that have a bimodal distribution. I have used the following
functions, in particular the ms() function, to estimate the parameters: two
means, two standard deviations, and one proportion. Here is the code I've
been using in S:
btmp.bi <- function(vec, p, m1, m2, sd1, sd2) { (exp(p)/(1+exp(p)))*dnorm(vec,mean=m1,sd=abs(sd1))+ (1-(exp(p)/(1+exp(p))))*dnorm(vec,mean=m2,sd=abs(sd2)) } btmp11 <- ms( ~ - sum(log((btmp.bi(btmp1$Temp, p, m1, m2, s1, s2)))), start = list(p = 0.4, m1 = 38, m2 = 40, s1 = 1, s2 = 1), control = list(maxiter = 200))
I have looked in the archives and tried various alternatives, especially
optim(), but so far have had nothing but frustration. I've been running this
in a semi-automated program on several hundred datasets a few times each
month for several years now. I would like to figure out how to move this to
R. Thank you for any help you might offer.
================================================================== George W. Gilchrist Email #1: [EMAIL PROTECTED] Department of Biology, Box 8795 Email #2: [EMAIL PROTECTED] College of William & Mary Phone: (757) 221-7751 Williamsburg, VA 23187-8795 Fax: (757) 221-6483 http://gwgilc.people.wm.edu/
______________________________________________
[EMAIL PROTECTED] mailing list
https://stat.ethz.ch/mailman/listinfo/r-help
PLEASE do read the posting guide! http://www.R-project.org/posting-guide.html
______________________________________________ [EMAIL PROTECTED] mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide! http://www.R-project.org/posting-guide.html
