[R] Estimating parameters for a bimodal distribution

George W. Gilchrist gwgilc at wm.edu
Thu Sep 16 16:59:35 CEST 2004

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)
    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: gwgilc at wm.edu
Department of Biology, Box 8795          Email #2: kitesci at cox.net
College of William & Mary                    Phone: (757) 221-7751
Williamsburg, VA 23187-8795                    Fax: (757) 221-6483

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