solving a ODE using ode45 or etc. with certain number of timestepping

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Hossein
Hossein on 16 Jun 2015
Answered: Walter Roberson on 16 Jun 2015
Hi everybody,
I want to solve an ODE using Adams-Bashforth 4th order method which needs the initial values of previous steps so I need to solve the ODE 4 or 5 times using other method such as Runge-Kutta. As far as ode45 is an adaptive time-stepping solver in order to save computation time has anybody any suggestion how can I make solver to do solving for just 4 or 5 times and then break it?
many tnx in advance.

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Answers (2)

Torsten
Torsten on 16 Jun 2015
Use the Runge-Kutta method to calculate 3 data points in addition to the initial condition:
for i = 1:3
k1 = f(t,y);
k2 = f(t+h/2, y+h/2*k1);
k3 = f(t+h/2, y+h/2*k2);
k4 = f(t+h, y+h*k3);
y = y+h/6*(k1 + 2*k2 + 2*k3 + k4);
t = t + h;
yn(1,i+1) = y;
end
Best wishes
Torsten.
  2 Comments
Hossein
Hossein on 16 Jun 2015
dear torsten tnx for the answer but it can not help me because I prefer using ode45 routin based on some oder problems and complexity and my question refers to adjusting number of steps just in ode45.
Torsten
Torsten on 16 Jun 2015
Well, you can set h, 2*h and 3*h as output times for the solution from ODE45 and feed your Adams routine with these values.
Best wishes
Torsten.

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Walter Roberson
Walter Roberson on 16 Jun 2015
Configure an OutputFcn option that tests the number of function calls from the information structure passed in and sets the termination flag appropriately.

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