combining ODE_FUNC and EVENT_FUNC for ODE solvers

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Chris 2014-2-21

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https://ww2.mathworks.cn/matlabcentral/answers/117121-combining-ode_func-and-event_func-for-ode-solvers

回答： Torsten 2015-7-6

I'm solving a non-stiff non-linear ODE problem using matlab's ODE23/ODE45 solvers. I have a transition in the model which I handle with an EVENT_FUNC. The value X that the EVENT_FUNC checks requires a sizable calculation.

My problem is that I already need to calculate X in my ODE_FUNC. Because the EVENT_FUNC is a separate thing, I have to calculate X twice which is not efficient.

My question is; is there any way to combine the ODE_FUNC and EVENT_FUNC such that the ODE_FUNC returns X together with all the other 2 parameters required by the EVENT_FUNC such that I don't have to perform the same computation twice.

Any suggestions / solutions are much appreciated.

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Answer 1

Torsten 2015-7-6

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https://ww2.mathworks.cn/matlabcentral/answers/117121-combining-ode_func-and-event_func-for-ode-solvers#answer_185092

Define X as global in ODE_FUNC and EVENT_FUNC.

Then check whether you can use the (last) value for X calculated in ODE_FUNC also in EVENT_FUNC (i.e. whether t and y as input parameters are the same).

Best wishes

Torsten.