Message-ID: <e8h0d9-ao4.ln1@news.jonasstein.de>
Date: 2012-07-11T15:04:14Z
From: Jonas Stein
Subject: nls problem: singular gradient
Why fails nls with "singular gradient" here?
I post a minimal example on the bottom and would be very
happy if someone could help me.
Kind regards,
###########
# define some constants
smallc <- 0.0001
t <- seq(0,1,0.001)
t0 <- 0.5
tau1 <- 0.02
# generate yy(t)
yy <- 1/2 * ( 1- tanh((t - t0)/smallc) * exp(-t / tau1) ) + rnorm(length(t))*0.01
# show the curve
plot(x=t, y=yy, pch=18)
# prepare data
dd <- data.frame(y=yy, x=t)
nlsfit <- nls(data=dd, y ~ 1/2 * ( 1- tanh((x - ttt)/smallc) * exp(-x / tau2) ), start=list(ttt=0.4, tau2=0.1) , trace=TRUE)
# get error:
# Error in nls(data = dd, y ~ 1/2 * (1 - tanh((x - ttt)/smallc) * exp(-x/tau2)), :
# singular gradient
--
Jonas Stein <news at jonasstein.de>