# [R] nlminb--lower bound for parameters are dependent on each others

From: Kyeongmi Cheon <katie.cheon_at_gmail.com>
Date: Thu, 24 Jul 2008 20:02:08 -0700 (PDT)

Hello
I'm trying to solve two sets of equations (each set has four equations and all of them share common parameters) with nlminb procedure. I

minimize one set and use their parameters as initial values of other set, repeating this until their parameters become very close to each other.

I have several parameters (say,param1, param2) and their constraints are given as inequality and depend on each other. For example, param1>=0, param1 + param2*c1>=0 (c1 is a known positive constant)

When I wrote my program as:

...

myfunction1 <-function(param ){..}
myfunction2 <-function(param ){..}

#param1=param[1]
#param2=param[2]
...

while (difference.Params>eps){
...

res1 <- nlminb(param.new2, myfunction1, lower = c(0, -c1/res1\$par[1]), upper = Inf)
param.new1<-res1\$par

res2 <- nlminb(param.new1, myfunction2, lower = c(0, -c1/res2\$par[1]), upper = Inf)
param.new2<-res2\$par

difference.Params <-max(abs(param.new1-param.new2))

}

I got error message:
Error in -res1\$par[1] : invalid argument to unary operator Is there any way to implement this constraint? Thank you for your help in advance.
Kyeongmi

Kyeongmi,

University of Memphis

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