Torsten
Posts:
1,439
Registered:
11/8/10


Re: How to get second derivatives using ode45
Posted:
Apr 30, 2013 10:41 AM


"stanley ontario" wrote in message <klok4d$fjp$1@newscl01ah.mathworks.com>... > > > vib_equ returns the first and second derivative of Y(:,1) in dy(1) and dy(2) as well as the first and second derivative of Y(:,3) in dy(3) and dy(4). So what's the problem ? > > > > Best wishes > > Torsten. > > > > Thank you for your answer. > > My problem is that I would like to call vib_equ outside the ode45, but if I do so, I have an error implying that there are undefined variables. > > For example if I want to plot both acceleration I need the values of dy(2) and dy(4), but I don't know how to call them.
For i=1:numel(t_vec) y(1)=Y(i,1); y(2)=Y(i,2); y(3)=Y(i,3); y(4)=Y(i,4); t=t_vec(i); dy=vib_equ(t,y,c_s_f,c_s_r,v_val,F_d_val,m_c,I_g_c,l,l_f,l_r,u_f,u_f_dot,v,L,i_d); Y_acc(i,1) = dy(2); Y_acc(i,2) = dy(4); end
does not work ?
(Of course you will have to supply the correct values for the variables in your calling list to vib_equ)
Or use the OutputFcn facility during the computation with ode45.
Best wishes Torsten.

