model2ssfun: Generate a sum of squares objective function from a nonlinear...
In nlmrt: Functions for Nonlinear Least Squares Solutions

Description Usage Arguments Details Value Author(s) References See Also Examples

Given a nonlinear model expressed as an expression of the form lhs ~ formula_for_rhs and a start vector where parameters used in the model formula are named, attempts to build the the R function for the residual sum of squares. As a side effect, a text file with the program code is generated.

1	model2ssfun(modelformula, pvec, funname="myss", filename=NULL)

`modelformula`	This is a modeling formula of the form (as in `nls`) lhsvar ~ rhsexpression for example, y ~ b1/(1+b2exp(-b3tt)) You may also give this as a string.
`pvec`	A named parameter vector. For our example, we could use start=c(b1=1, b2=2.345, b3=0.123) WARNING: the parameters in the output function will be used in the order presented in this vector. Names are NOT respected in the output function.
`funname`	The (optional) name for the function that is generated in the file named in the next argument. The default name is 'myss'.
`filename`	The (optional) name of a file that is written containing the (text) program code for the function. If NULL, no file is written.

None.

An R function object that computes the sum of squares of the residuals of the nonlinear model at a set of parameters.

John C Nash <nashjc@uottawa.ca>

Nash, J. C. (1979, 1990) _Compact Numerical Methods for Computers. Linear Algebra and Function Minimisation._ Adam Hilger./Institute of Physics Publications

Function nls(), packages optim and optimx.

  # a test
  y <- c(5.308, 7.24, 9.638, 12.866, 17.069, 23.192, 31.443, 38.558, 
      50.156, 62.948, 75.995, 91.972)  # for testing
  tt <- seq_along(y)  # for testing
  f <- y ~ b1/(1 + b2 * exp(-1 * b3 * tt))
  p <- c(b1 = 1, b2 = 1, b3 = 1)
  myfn <- model2ssfun(f, p)
  cat("myfn: \n")
  print(myfn) # list the function
  cat("Compute the function at several points\n")
  ans <- myfn(p, tt = tt, y = y)
  print(ans) # should be  23520.58
  bnew <- c(b1 = 200, b2 = 50, b3 = 0.3)
  anew <- myfn(prm = bnew, tt = tt, y = y)
  print(anew)# should be  158.2324
  
  cat("Test with vector of un-named parameters \n")
  bthree <- c(100, 40, 0.1)
  athree <- try(myfn(prm = bthree, tt = tt, y = y))
  print(athree) # should be 19536.65