To predict from Weight~alpha*Length^beta you need to specify Length, not
Weight. It is most likely finding Length from your workspace.
On Thu, 12 Jun 2008, Ranney, Steven wrote:
I keep running up against the same error when I try to plot a line from a nls
model. The data is fisheries length/weight data. Code follows:
require(graphics)
pow = nls(Weight~alpha*Length^beta, data=wae,
start=list(alpha=0.0000001, beta=3.0), trace=TRUE)
predict(pow)
plot(Weight~Length, data = wae, pch=19,
xlab="Length (mm)", ylab="Weight (g)",
xlim = c(150,1000), ylim = c(0, 10050))
mod = seq(150, 1000)
lines(mod, predict(pow, list(Weight = mod)))
The error I get after I submit the final line is:
Error in xy.coords(x, y) : 'x' and 'y' lengths differ
Like my last post, I'm certain there's something simple I'm overlooking. I've
been able to get this to work on other data sets, but _how_ I've been able to
get this to work, I'm unsure.
Thanks for your help,
SR
Steven H. Ranney
Graduate Research Assistant (Ph.D)
USGS Montana Cooperative Fishery Research Unit
Montana State University
PO Box 173460
Bozeman, MT 59717-3460
phone: (406) 994-6643
fax: (406) 994-7479
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