[R] nls and discontinuous functions

From: Luis Orlindo Tedeschi <luis.tedeschi_at_hotmail.com>
Date: Fri, 30 Nov 2007 08:25:16 -0600


Folks; I have looked for this subject extensively using all the resources I have available and could not find a solution; therefore I am sending you this email seeking for help. I need to solve a discontinuous nonlinear function, but R 2.6 keeps giving me an error. Below is a simple example:  

f <- function (t,k,l,u) { r0<-346.1 x<-t-l if (x<0) r0 else (r0-u)*exp(-k*x)+u }prof1<-read.table("c:\\data.txt", header=TRUE)results<-nls(y1~f1(t,k,l,u), data=prof1, start=list(k=0.05, l=4, u=154))  

Errors I am getting are:    

Error in qr(.swts * attr(rhs, "gradient")) : dims [product 3] do not match the length of object [10]In addition: Warning messages:1: In if (x < 0) r0 else (r0 - u) * exp(-k * x) + u : the condition has length > 1 and only the first element will be used2: In if (x < 0) r0 else (r0 - u) * exp(-k * x) + u : the condition has length > 1 and only the first element will be used3: In if (x < 0) r0 else (r0 - u) * exp(-k * x) + u : the condition has length > 1 and only the first element will be used4: In if (x < 0) r0 else (r0 - u) * exp(-k * x) + u : the condition has length > 1 and only the first element will be used5: In if (x < 0) r0 else (r0 - u) * exp(-k * x) + u : the condition has length > 1 and only the first element will be used6: In .swts * attr(rhs, "gradient") : longer object length is not a multiple of shorter object length Data file is this one    

    t y1
1 0 346.12 3 343.13 6 327.44 12 280.95 18 242.76 24 228.67 36 193.48 48 174.29 72 164.810 96 152.0    

Any help?  

Thanks a lot  

Luis


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