In Ode15s, how do I break the time span into smaller intervals and call the solver twice, so that the integration proceeds faster?

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Ziwei Liu 2019-2-27

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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/447254-in-ode15s-how-do-i-break-the-time-span-into-smaller-intervals-and-call-the-solver-twice-so-that-th

评论： Ziwei Liu 2019-2-27

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Hi, can anyone explain these lines from the Matlab website to me?

and

I understand how splitting the total time span into small intervals can speed up ODE. But in order to implement this method, how exactly do I "call the solver twice"? How to combine the outputs from each call into one? Say my total time span is

tspan=[t0 tf];

and I break it into

tspan1=[t0 t1];
tspan2=[t1 tf];

If I directly call the solver twice like the following,

% Method 1
[ta,y1]=ode15s(@odefun,tspan1,initialCond,solverOptions,additionalParams);
[tb,y2]=ode15s(@odefun,tspan2,initialCond,solverOptions,additionalParams);

I will get two outputs. But all I need is just one, like the [t, y] below.

% Method 2
[t,y]=ode15s(@odefun,tspan,initialCond,solverOptions,additionalParams);

How can I combine the results from method 1 and get only one output? It would be best if there's code or examples. Thank you.

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Answer 1

Torsten 2019-2-27

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此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/447254-in-ode15s-how-do-i-break-the-time-span-into-smaller-intervals-and-call-the-solver-twice-so-that-th#answer_362943

tspan1=[t0 t1];
[ta,y1]=ode15s(@odefun,tspan1,initialCond,solverOptions,additionalParams);
initialCond=y1(end,:);
tspan2=[t1 tf];
[tb,y2]=ode15s(@odefun,tspan2,initialCond,solverOptions,additionalParams);
t=[ta(1:end-1);tb];
y=[y1(1:end-1,:);y2];