Hello CaptainBlack!

Thank you so much for your helpful comment!

I tried it but it still doesn't work.

Code:

function dx = ivp(t, x)
dx = \dot{x} * x;

clearly represented, I wrote $\displaystyle \dot{x}$ for

$\displaystyle

\dot{\bold{x}}=\left[ \begin{array}{c}

\bold{x}_3\\

\bold{x}_4\\

\bold{x}_1-2\bold{x}_4-0.9(\bold{x}_1+0.1)/D_1-0.1(\bold{x}_1-0.9)/D_2 \\

\bold{x}_2-2\bold{x}_3-0.9\bold{x}_2/D_1-0.1\bold{x}_2/D_2

\end{array} \right]

$

then:

[t, x] = ode45(@ivp, [0, 10], [??,??,??,??] )

where $\displaystyle t \in [0, 10]$ and ?? = [x_3(0); x_4(0);, ...(0); ...(0)]

this is stupid, but I don't know the initial values :-(