[R] rls() fails on function calling spline()

[Hengstberger Florian]

Hello everybody

I want to use rls() on a multi-dimensional function, where parts of it are modeled using a spline.
I tried to condense my problem into the following code example,
which tries to fit the y-values of a spline interpolation:

---------------------------------------------------------------------------
rm(list=ls(all=TRUE))

x<-c(1,2,3,4,5,6,7,8,9)
y<-x^2

f<-function(x,c1,c3,c6,c9){
ys<-spline(c(1,3,6,9),y=c(c1,c3,c6,c9),xout=x)$y
print(ys)
print(c1)
return(ys)
}

print('Function evaluation')

f(x,1,1,1,1)
f(x,1,1,1,2)

print('Fit')

fit<-nls(y~f(x,c1,c3,c6,c9),start=list(c1=1,c3=1,c6=1,c9=1),
control=nls.control(maxiter=5))

-------------------------------------------------------------------

When I run the program, nls() does not change the parameters c1,c3,c6,c9,
and the iteration does no converge (here stopped after maxiter).
Moreover, ys always contains y=x^2 for some odd reason.
Using splinefun instead does no change the result.

Is there something with scope rule I do not understand?
Any ideas?

Kind regards
Florian Hengstberger

DI Dr. FLORIAN HENGSTBERGER
Energy Department
Sustainable Thermal Energy Systems

AIT Austrian Institute of Technology GmbH
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