[R] a nlm() question

[Jiang Peng]

  Dear R listers,
   I have a very annoying problem using nlm().
   I want to find the minimizer of my target function, if written in  
\LaTeX is
   f(\mu1,\mu2,\sigma1,\sigma2) = \sum_i^n( w_ig_t(z_i) ), where  
g_t(z) is a pdf of  bivariate normal distribution and z_i is my samples.
    I cannot get the estimation result generated by nlm(), and I got  
the following errors

   "
Error in nlm(foo, theta.start, hessian = TRUE) :
   non-finite value supplied by 'nlm'
   "

from time to time( If I ran the code second time , it does not have  
the error .) I am new to R so I don't know if there is any debug  
method of R code. i hope somebody can help me out .

Thanks in advance.

------------------------
Jiang Peng, Ph.D. Candidate
Department of mathematics &
Antai college of Economics and management
Shanghai Jiao Tong University
Address: Room 127, #3 Building, Xuhui Campus
E-mail: jp021 at sjtu.edu.cn
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