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

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Day 2023-3-4

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https://ww2.mathworks.cn/matlabcentral/answers/1922885-the-fluctuation-of-the-content-of-a-species-between-negative-and-positive

评论： Arthur Goldsipe 2023-3-6

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?

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Jacopo Biasetti 2023-3-6

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 2023-3-6

Thank you so much

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Answer 1

Arthur Goldsipe 2023-3-6

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https://ww2.mathworks.cn/matlabcentral/answers/1922885-the-fluctuation-of-the-content-of-a-species-between-negative-and-positive#answer_1186470

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.

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Day 2023-3-6

@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 2023-3-6

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.

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