SimBiology error with e^time in reaction rate

I've got a pretty complicated differential equation to describe absorption from a dosing site to the central compartment, part of which contains the term e^(-ka*Time). I've tried using it in the reaction rate itself (as exp(-ka*Time)) and as a rate rule, but I've been getting errors, either that SimBiology can't perform dimensional analysis due to the exp(), or that it can't evaluate the reaction rate at t=0.0000. Is there a way I can get SimBiology to use this term in my reaction rate?

Answer 1

[Arthur Goldsipe]

Hi,

The message about being unable to perform dimensional analysis is a warning, not an error. Your simulation results should be fine. You just need to manually check your units in the rule and make sure that the argument of exp is dimensionless. See the "Tip" on the reference page for DimensionalAnalysis.

I'm not sure what you mean by "it can't evaluate the reaction rate at t=0.0000". Can you provide more details, such as the exact error message and some sort of reproduction steps? Ideally, if you can attach your model to the question that would make it easier for us to help you.

-Arthur

[Colin Cess]

Here's the error:

Source Type: Task Message: Error evaluating reaction rate (from reaction Absorption) at t=0.0000. Check MATLAB expressions and user-defined functions for errors.

The reaction is DosingSite.Dose -> Central.Drug, with those being milligrams. The reaction rate is "Dose*(frel*f1*ka*exp(-ka*Time))". ka is 1/day, and everything else is unitless.

I've attached a model that contains the error-causing reaction.

[Arthur Goldsipe]

Ahhh. The problem is that you used "Time" instead of "time". SimBiology is case-sensitive. After I changed the case, the model simulated for me.

[Colin Cess]

...wow. Thanks a lot! Did not know that.