Hi fellow R users,

I'm trying to fit a model using nls with the following model definition:

y(t+1)=(th1*x1 + R1*x2) * exp(a1*x3) + (1-th1*x1 + R1*x2)*y(t)

y is the dependent variable (note on both sides of eq) and the x's represent the regressors.
th1, R1 and a1 are parameters to be estimated. The problem is non- linear and hence why I'm trying to fit using the well used "nls" function.

To fit the model I would like to be able to use the formula interface rather than build my own ugly function definition.
Any ideas if this is achievable and if not any ideas on how to fit this model?


Many thanks,

Wayne




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Wayne Jones
Statistics & Chemometrics
Shell Global Solutions (UK)
Shell Technology Centre Thornton
P.O. Box 1, Chester CH1 3SH, United Kingdom
Tel: +44 (0) 151 373 5977 Mobile: +44 (0) 7896 536026
Email: Wayne.W.Jones@shell.com<mailto:Wayne.W.Jones@shell.com>
Intranet: Statistics and Chemometrics - Shell Wiki<http://sww.wiki.shell.com/wiki/index.php/Statistics_and_Chemometrics>
Internet: Shell Global Solutions<http://www.shell.com/globalsolutions>

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