After a few days of work, I think I nearly have it.
Unfortunately, theta is unchanged after I run this (as a script from a
file). I thought that theta would contain the fitted parameters.
The goal here is to find the least squares fit according to the function
defined as "rss" subject to the constraints defined as ui and ci.
I defined ui and ci to (hopefully) force par2 and par3 into the range 0.0
<= par2 <= 1.0 and 0.0 <= par3 <= 1.0.
I am not at all sure that ui and ci are defined correctly.
The call to constrOptim returns normally, but without a solution
(apparently).
Any suggestions appreciated.
Thanks
Stu
# data
y <-
c(0.111111111111111,0.0921052631578947,0.0564516129032258,0.0608108108108108
,0.0128205128205128,0.0136078431372549);
x1 <-
c(0,0.978723404255319,0.087378640776699,0.549295774647887,0.0596026490066225
,0.61578947368421);
x2 <- c(1,3,4,5,6,7);
x3 <- c(3600,169200,185400,255600,271800,342000);
observs <- data.frame(y, x1, x2, x3);
# function definition
rss <- function(par, y, x1, x2, x3) {
par1 <- par[1]
par2 <- par[2]
par3 <- par[3]
ressq <- (y - par1 * (x1 + 1) * x2^(-par2) * x3^par3)^2
sum(ressq)
}
#call to optimizer
opti <- constrOptim(c(0.5, 0.5, 0.1), rss, NULL, ui = rbind(c(0, 0), c(1,
0), c(0, 1)), ci = c(0, 1, 1));
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