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

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.

Answer 1

[Torsten]

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.

[Hossein]

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]

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.

Answer 2

[Walter Roberson]

Configure an OutputFcn option that tests the number of function calls from the information structure passed in and sets the termination flag appropriately.