is it possible to make an inverted prediction with an nlsList object?-CodePudding

I have fitted an nlsList model with my data and now I need to estimate the value of "x" corresponding to a given "y" using my model.

I have tried with "invest" from investr package, but it works only with objects from class lm, glm, nls, or lme.

CodePudding user response：

When posting to SO the question needs to provide a reproducible example for testing including input, code and expected output. See the instructions at the top of the r tag page. I have done it for you this time in the Note at the end.

Create a function pred which predicts Sepal.Width given Sepal.Length and Species. Then we can use uniroot as shown:

library(nlme)
# run code in Note

pred <- function(Sepal.Length, Species) {
  predict(fm, list(Sepal.Length = Sepal.Length, Species = Species))
}
uniroot(function(x) pred(x, "virginica") - 3, c(-10, 10))

This gives the following which says that the Sepal.Length corresponding to a Sepal.Width of 3 and Species virginica is 6.7168.

$root
[1] 6.716803

$f.root
   virginica 
2.524802e-06 
attr(,"label")
[1] "Predicted values"

$iter
[1] 5

$init.it
[1] NA

$estim.prec
[1] 6.103516e-05

Note

Reproducible example using built=in iris data set follows. We assume that given Sepal.Width = 3 and Species = "virginica" that we want to find Sepal.Length.

library(nlme)
fm <- nlsList(Sepal.Width ~ a * exp(Sepal.Length*b) | Species, data = iris, 
  start = list(a = 0.5, b = 0.5))