[R] nls newbie: help approximating Weibull distribution

Dr. Mirko Luedde Mirko.Luedde at computer.org
Mon Jul 2 14:10:51 CEST 2001

Hi folks, 

I tried to retain the Weibull distribution using the `nls' function
and proceeding along the lines of the example provided in the
`SSweibull' help (at least I thought so):

	t <- (1:200)/100
	v <- pweibull(t, shape=3, scale=1)
	df <- data.frame(Time=t, Value=v)
	Asym <- 1.0; Drop <- 1.0; lrc <- 0; pwr <- 1
	df.estimate <- nls(Value ~ SSweibull(Time, Asym, Drop, lrc, pwr), data=df)

But this yields the error message "Error in qr.solve(QR.B, cc) :
singular matrix `a' in solve".

Any hints? 

Thanks, Mirko. 

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