Date: Apr 30, 2013 10:41 AM
Author: Torsten
Subject: Re: How to get second derivatives using ode45
"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.