The fluctuation of the content of a species between negative and positive

The model I am developing in Simbiology includes a drug species in which large repeated amounts of doses are injected. It has no other input parameters.

Why does the content if the drug species fluctuates between negative and positive values; although the content of the species is still large, i.e. far away from zero?

[Jacopo Biasetti]

Hi,

One possibility is that your system of equations is stiff. Stiff systems usually result in oscillations when not solved correctly. Try using a stiff solver, e.g., ode15s, and also reduce the timestep.

Jacopo

[Day]

Thank you so much

Answer 1

[Arthur Goldsipe]

Can you share the model? As Jacopo mentions in the comment above, this is likely due to the difficult of solving the underlying differential equations for this model. In the absence of more details, the only thing I can suggest is to look at this doc page.

[Day]

@Arthur Goldsipe

I accepted the answer.

Could you please help me in solving the following:

I set a trigger event in Simbiology that when 'X' species exceeds a certain mass then X= k*Time, where k is a parameter.

However, the condition is achieved at n of time, I received an error says that

Error computing event function at t=n

How should I solve this problem?

[Arthur Goldsipe]

I recommend creating a new MATLAB Answers question, and sharing detailed reproduction steps. Ideally, share your code or project. Without these details, it's hard to help you.