let say I have below data
Data = structure(list(col1 = c(31, 66, 88, 123, 249, 362, 488, 610,
730, 842), col2 = c(2101.58953918969, 2103.57391509821, 2100.3292541732,
2101.64107993765, 2100.51743895393, 2100.16708521627, 2102.1992412748,
2101.06516854423, 2101.87929065226, 2101.25318636023)), row.names = c(NA,
-10L), class = "data.frame")
Now I want to fit a non-linear equation as below -
library(stats)
nls(col2 ~ x1 + x2 / (1 + exp(-x3 * (col1 - x4))), data = Data, start = list(x1 = 0, x2 = 0, x3 = 0, x4 = 0), algorithm = "plinear")
However with this I am getting below error -
Error in qr.qty(QR.rhs, .swts * ddot(attr(rhs, "gradient"), lin)) :
NA/NaN/Inf in foreign function call (arg 5)
Can you please help me to understand what went wrong in my approach?
I want to use only base package to fit this equation as I can not download any contributed package from internet in my system.
Any pointer will be highly appreciated.
If I use SSfpl
with your current data I can get an answer.
n1 <- nls(col2 ~ SSfpl(col1, A, B, m, s), data=Data)
pframe <- data.frame(col1=seq(0,900,length=101))
pframe$col2 <- predict(n1, newdata=pframe)
library(ggplot2); theme_set(theme_bw())
ggplot(Data, aes(col1,col2)) + geom_point() + geom_smooth() +
geom_line(data=pframe, colour="red")
The parameterization is not quite the same as yours:
A B m s
2001.56354 2002.06645 642.30178 20.76013
Based on x1 + x2 / (1 + exp(-x3 * (col1 - x4)))
,
I believe x4
= m
(midpoint), x3
= s
(scale), x1
= A
(left asymptote), and x2
= B-A
(B
is the right asymptote).