That's odd, it works just fine for me
(R 2.6.1, i486-pc-linux-gnu)
Can you send the results of sessionInfo() ?
# Observed data
Prepens.caughtintraps = c(94,45,71,64,71,31,16,19,27,16,113)
# Numbers of seeds released
Prepens.released = 1250
distances = c(2,3,4,5,7.5,10,12.5,15,17.5,20,25)
totalseedscaught = sum(Prepens.caughtintraps)
Pcatch = totalseedscaught/Prepens.released
## minor tweak: this is more efficient, gives same answer
cumsumcaught <- rev(cumsum(rev(Prepens.caughtintraps)))
res.nls <- nls(cumsumcaught ~
Pcatch*Prepens.released*(1-pweibull(distances,k,l)),
start = list(k=1,l=12), trace=TRUE)
## slightly more accurate -- use lower.tail instead of 1-pweibull()
## but makes no difference in this case
res.nls <- nls(cumsumcaught ~
Pcatch*Prepens.released*
pweibull(distances,k,l,lower.tail=FALSE),
start = list(k=1,l=12), trace=TRUE)
13122.82 : 1 12
11783.76 : 1.045207 12.668148
11774.70 : 1.035480 12.676250
11774.54 : 1.036564 12.679938
11774.54 : 1.036398 12.679737
11774.54 : 1.036420 12.679783
11774.54 : 1.036417 12.679778
Nonlinear regression model
model: cumsumcaught ~ Pcatch * Prepens.released * pweibull(distances, k,
l, lower.tail = FALSE)
data: parent.frame()
k l
1.036 12.680
residual sum-of-squares: 11775
Number of iterations to convergence: 6
Achieved convergence tolerance: 1.388e-06
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