[R] question about model formula

Michael A. Miller mmiller3 at iupui.edu
Thu Mar 6 19:32:40 CET 2003

Dear R Gang,

I'm interested in using R and the nls package for fitting kinetic
models.  I'm having some difficulty getting a model specified for
nls though.  The math for the model that I want to fit is

   dg(t)/dt = K1 f(t) - k2 g(t)

where g(t) and f(t) are measured data at a sequence of times t.
K1 and k2 are the parameters of the model.  If I solve this, the
solution is

  g(t) = K1 \int_0^t f(t') \exp(-k2(t-t')) dt'

and I'm not sure how to write a formula in R that I can pass to
nls that will handle both the implicit loop over the data values
of t and the interpolation and numeric integration over t'.

Can anyone help me to get this properly coded for R?


Michael A. Miller                               mmiller3 at iupui.edu
  Imaging Sciences, Department of Radiology, IU School of Medicine

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