ode45 with a function that change with time

I have a body that is subjected to an acceleration for a time duration of "tp". After this time the acceleration go to zero and the velocity is constant. So I have introduced an if on the velocity value. The problem is that the result is not a step: I have a transitory before obtain a constant value for the velocity. In the follow you can read the code:

Main:

v = 0; %m/s initial velocity

x = 0; %m initial position

X0 = [x,v]; %initial status

time = 0:0.0001:10; %integration time

[t,X] = ode45(@int,time,X0);

Function:

v= sqrt(K/m)*d;

j= X(2)

if j<v F = K*d;

else F = 0;

end

dX = zeros(2,1);

dX(1) = X(2);

dX(2) = F/m;

Thank you in advance for any suggestion

Answer 1

[Mischa Kim]

Nashira, one approach is to use two different ode functions. Use the first one to integrate over the time interval [0,tp] and the second one for the interval [tp,10]. The initial conditions for the second integration are the final conditions of the first.

[Torsten]

@Mischa Kim: Although the OP claims that the equations change at time tp, the code indicates that this time instant is unknown in advance. I suggest to use the event facility of ODE45. The ballode example in the documentation is a good starting point.

Best wishes

Torsten.

[Nashira]

So, it is not possible to change the integrated function in ode45, I have to use 2 ode45 and merge the final graph... ok! thank you for your answers and suggestions!