[R] curve fitting problem

[pieterprovoost at gmail.com]

I'm trying to fit a function y=k*l^(m*x) to some data points, with  reasonable starting value estimates (I think). I keep getting "singular matrix 'a' in solve".

This is the code:

ox <- c(-600,-300,-200,1,100,200)
ir <- c(1,2.5,4,9,14,20)
model <- nls(ir ~ k*l^(m*ox),start=list(k=10,l=3,m=0.004),algorithm="plinear")
summary(model)
plot(ox,ir)
testox <- seq(-600,200,length=100)
k <- 10
l <- 3
m <- 0.004
testir <- k*l^(m*testox)
lines(testox,testir)

Any thoughts?
Thanks!

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