search for: scal1

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2010 Jan 13
1
Problem fitting a non-linear regression model with nls
Hi, I'm trying to make a regression of the form : formula <- y ~ Asym_inf + Asym_sup * ( (1 / (1 + (n1 * (exp( (tmid1-x) / scal1) )^(1/n1) ) ) ) - (1 / (1 + (n2 * (exp( (tmid2-x) / scal2) )^(1/n2) ) ) ) ) which is a sum of the generalized logistic model proposed by richards. with data such as these: x <- c(88,113,128,143,157,172,184,198,210,226,240,249,263,284,302,340) y <- c(0.04,0.16,1.09,2.65,2.46,2.43,1.88,2.42...
2004 Jul 28
0
Modelling compound logistic growth curves
...t allows one to decompose growth curves into a series of logistic equations, I attempted to do the same thing in R. SIMULATED DATA Time <- 1:200 pop.size <- SSlogis(Time,10,20,5) + SSlogis(Time,20,100,20) + rnorm(length(Time)) MY ANALYSIS results <- nls(size ~ SSlogis(Time, Asym1, xmid1, scal1) + SSlogis(Time, Asym2, xmid2, scal2), start = list(Asym1=5, xmid1=15, scal1=30, Asym2=25, xmid2=67, scal2=25)) THE RESULT I get the error message: Error in nls(size ~ SSlogis(Time, Asym1, xmid1, scal1) + SSlogis(Time, : step factor 0.000488281 reduced below `minFactor' of 0.000976563...
2004 Aug 16
0
Multiple logistic curves
...f growth curves into a series of logistic equations, I attempted to do the same thing in R. #SIMULATED DATA Time <- 1:200 pop.size <- SSlogis(Time,10,20,5) + SSlogis(Time,20,100,20) + rnorm(length(Time)) ts.plot(pop.size) #MY ANALYSIS results <- nls(pop.size ~ SSlogis(Time, Asym1, xmid1, scal1) + SSlogis(Time, Asym2, xmid2, scal2), start = list(Asym1=5, xmid1=15, scal1=30, Asym2=25, xmid2=60, scal2=25)) THE RESULT I get the error message: Error in nls(size ~ SSlogis(Time, Asym1, xmid1, scal1) + SSlogis(Time, : step factor 0.000488281 reduced below `minFactor' of 0.000976563...
2010 Feb 03
1
comparison of parameters for nonlinear regression
Hi, I have two series of data set (it's measurment of growth but under two different conditions). To model these data I use the same function which is : formula <- y ~ Asym_inf + Asym_sup * ( (1 / (1 + (n1 * (exp( (tmid1-x) / scal1) )^(1/n1) ) ) ) - (1 / (1 + (n2 * (exp( (tmid2-x) / scal2) )^(1/n2) ) ) ) ) After the estimation of the parameters thanks to "nls", I have 2 models. The idea is I want to compare this 2 models and particularly I want to know if the parameters are different are not beteween this 2 model...