Hello,
I'm trying to use the differential equation solver in OpenBUGS ( function ode ) to adjust a differential equation to a data-set.
I have been playing with the examples given in the installation and this works quite well.
However my differential equation is in the form of :
D(C[1], t) <- a*(log((b-c)/(C[1]-c))))*(C[1]-c)
I'm getting regular error messages from OpenBUGS when I try to run this model, either concerning the differential equation solver (Runge Kutta as far as I could gather from the extended error windows) or for multiplication or concerning the logarithm.
As far as I can see most of these problems are based on the logarithm, which either gives an error message when the argument is negative or if infinite if it is zero.
Thus the problem is either that b-c or C[1]-c could be negative and thus the argument is negative
Or that one of the two substractions are zero.
If I introduce a function like "step" into the differential equation i also get an error related to the solver.
The best solution would be to programm a condition, which will avoid any parameter values that are not allowed for this equation.
As far as I could gather from my search on the net, this is not a simple problem in the OpenBUGS programming language.
Does anybody have any ideas on this ?
Thanks very much in advance for any hints
best regards
OliB
-------------------------------------------------------------------
This list is for discussion of modelling issues and the BUGS software.
For help with crashes and error messages, first mail [log in to unmask]
To mail the BUGS list, mail to [log in to unmask]
Before mailing, please check the archive at www.jiscmail.ac.uk/lists/bugs.html
Please do not mail attachments to the list.
To leave the BUGS list, send LEAVE BUGS to [log in to unmask]
If this fails, mail [log in to unmask], NOT the whole list
|