Sorry that I specified the x as
x=c(0, 0.4, 0.7, 1, 1.4, 1.6, 1.8, 2:10)
The error message is the same.
Thanks.
Hanna
----- Original Message -----
From: Yimeng Lu
To: r-help@stat.math.ethz.ch
Sent: Thursday, July 14, 2005 11:19 PM
Subject: problems with nls function
Hello,
I was trying to fit a generalized logistic curve and my code for testing
if the function "nls" is working is like this
#######
#define the generalized logistic curve function
glogit=function(a, b, c, m, t, x)
{
tmp = 1/(1 + t * exp(-b * (x - m)))^(1/t)
model.func = a + tmp * c
#define the gradient vector
Z = cbind(1, c*(x-m)*tmp^(t+1)*exp(-b*(x-m)), tmp, -c*b*exp(-b*(x-m))
*temp^(t+1), -c*tmp*(1/t)* (log(tmp) + tmp^(-t) * exp(-b(x-m))))
attr(model.func,"gradient")=Z
model.func
}
a= 0
b=3
c=6
m=2
t=0.75
x=c(1:10)
y=a + c/(1 + t * exp(-b * (x - m)))^(1/t) + rnorm(16, sd=0.01)
plot(data.frame(x=x, y=y), type = "p", col = "red")
nls(y ~ glogit(a, b, c, m, t, x), data=data.frame(y=y,x=x), start=list(a=1,
b=2, c=3, m=1, t=0, x), trace=T)
#####End.
When I ran this code, I got the error "Error in assign(i, temp, envir = env)
: attempt to use zero-length variable name". What does this error mean? How
should I fix it?
Many thanks.
Hanna Lu
Dept. of Biostatistics
Columbia University
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