[英]Sigmoidal Modeling in R
I am currently trying to model and plot a sigmoidal curve with a low amount of points. 我目前正在尝试建模和绘制具有少量点的S形曲线。
>myExperiment
V1 N mean
0.1 9 0.9
1 9 0.8
10 9 0.1
5 9 0.2
I am using the nlsLM
function from the minpack.lm
package. 我正在使用minpack.lm
包中的nlsLM
函数。
> nlsLM(mean2 ~ -a/(1 + exp(-b * (v1-o))))
Nonlinear regression model
model: mean2 ~ -a/(1 + exp(-b * (v1 - o)))
data: parent.frame()
a b o
-1.452 -0.451 1.292
residual sum-of-squares: 0.007017
Number of iterations to convergence: 27
Achieved convergence tolerance: 1.49e-08
Warning message:
In nlsLM(mean2 ~ -a/(1 + exp(-b * (v1 - o)))) :
No starting values specified for some parameters.
Initializing ‘a’, ‘b’, ‘o’ to '1.'.
Consider specifying 'start' or using a selfStart model
Using those starting values I receive this error. 使用这些起始值,我会收到此错误。
> nls(mean~-a/(1 + exp(-b * (v1-o))), start=list(a=-1.452, b=-0.451, o=1.292))
Error in nls(mean ~ -a/(1 + exp(-b * (v1 - o))), start = list(a = -1.452, :
step factor 0.000488281 reduced below 'minFactor' of 0.000976562
I am not well studied in stats to know if this is a syntax R error or a stats failure. 我对统计资料的研究不够深入,不知道这是语法R错误还是统计信息失败。 What am I doing poorly? 我做得不好吗?
-Thanks -谢谢
This looks like binomial dose-response data. 这看起来像二项式剂量反应数据。 In any case, I would propose a simpler model, like the two parameter log-logistic model, with asymptotes at 0 and 1. A lot of sigmoidal models have been coded up in the drc package. 无论如何,我都会提出一个更简单的模型,如两个参数的对数逻辑模型,渐近线分别为0和1。在drc包中已经编码了许多S形模型。
myExperiment = read.table(header = TRUE, text =
" V1 N mean
0.1 9 0.9
1 9 0.8
10 9 0.1
5 9 0.2")
library(drc)
m.ll2 <- drm(mean ~ V1,
data = myExperiment,
type = "binomial",
fct = LL.2(),
weights = N)
plot(m.ll2, ylim = c(0, 1))
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