Hello CaptainBlack!
Thank you so much for your helpful comment!
Quote:
Originally Posted by CaptainBlack  You will need to write a Matlab function to evaluate the derivative and pass that to ode45 (the derivative is now too complicated to be easily passed as an anonymous function).
(You cound simplify the derivative by collecting terms)
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I tried it but it still doesn't work.
Code:
function dx = ivp(t, x)
dx = \dot{x} * x;
clearly represented, I wrote
for
![\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]](http://www.mathhelpforum.com/math-help/latex2/img/97d6d60ae9bf84b85688225262d039ad-1.gif "\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
![t \in [0, 10]](http://www.mathhelpforum.com/math-help/latex2/img/1c75f0e0c25ae64c5fe7e65227bbcb32-1.gif "t \in [0, 10]")
and ?? = [x_3(0); x_4(0);, ...(0); ...(0)]
this is stupid, but I don't know the initial values :-(