Adding conditions / additional input to ode45 function

Question

yuval 2017-5-2

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https://ww2.mathworks.cn/matlabcentral/answers/338438-adding-conditions-additional-input-to-ode45-function

编辑： yuval 2017-5-5

Hello, I'm using ode45 and I want to be able to add an input ('i') which will determine a parameter in the function I put in the ode45:

[T,V] = ode45(@myfun,[0 20],vec_0);

and the function (shortened) is:

function dy = myfun(t,y)

dy=zeros(4,1);

if i==1

I_inj = 20;

elseif i==2

I_inj = 40;

% etc...

end

dy(1) = ...

dy(2) = ...

dy(3) = ...

dy(4) = ... + I_inj;

I've tried to add 'i' in the inputs of the function: function dy = hh(t,y,i) but I couldn't understand how to input 'i' in the ode45 function ( [T,V] = ode45(@myfun,[0 20],vec_0); ) I'll be happy to know how to do that or if there are other ways to set conditions to a function for ode45. Thanks a lot!

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Answer 1

Steven Lord 2017-5-2

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https://ww2.mathworks.cn/matlabcentral/answers/338438-adding-conditions-additional-input-to-ode45-function#answer_265420

While this documentation page uses fzero in its examples, the same techniques work for passing additional parameters into the ODE functions that you specify as the first input when you call ode45.

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yuval 2017-5-5

Thank you!

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Answer 2

yuval 2017-5-5

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https://ww2.mathworks.cn/matlabcentral/answers/338438-adding-conditions-additional-input-to-ode45-function#answer_265764

编辑：yuval 2017-5-5

For future reference, besides the solutions presented in the documentation page referenced by Steven Lord, I found another and somewhat simpler option, which is not mentioned in the help section of ode45. It is possible to add more parameters in this method:

extra_parameter=1;

options=odeset(...)

[T,V] = ode45(@my_fun,[0 20],[2 0],options,extra_parameter);

It only seemed to work if I defined 'options' (odeset), although I had no intention to, but otherwise it didn't take my extra parameter. That is, the following does not work:

[T,V] = ode45(@my_fun,[0 20],[2 0],extra_parameter);

Also, this is possible:

[T,V] = ode45(@(t,v) my_fun(t,v,extra_parameter),[0 20],[20 0]);