[R-sig-dyn-mod] Problem with simecol and ode - crash from R

[dave fournier]

Artificially bounding parameters reduces the differentiability
of the function and makes optimization slower or more difficult.
a better approach I think is to use implicit methods and fixed step size
for formulating the solution to the ODE.  See section 1-17 of the ADMB
manual for this approach applied to the Schaeffer-Pella-Tomlinson model.

  http://admb-project.googlecode.com/files/admb.pdf

That is the name used in fisheries for a generalization of the
logistic.  Using these ideas and ADMB it is possible to quickly fit
multi-parameter generalizations of these models.

The big advantages of the implict method are that it is numerically
stable and can use a larger step size.



-- 
David A. Fournier
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