How do i model a non linear differential equation in simulink?

Hello everyone

i´m new to simulink and trying to get accustomed to the platform. i am trying to model this in simulink:

and this is all i have so far

i don´t know how to proceed further. Can somebody help me?

[Nitya Patel]

Can you tell me what is?

[Karl-JR]

oh sorry, it´s "σ"

Answer 1

[Pramil]

Taking u(t) as unit step, you can shift x'''(t) one side and u^2(t) to the other and try the following :

where fcn is Matlab function block, having function :

function y = fcn(u)
y = u/(u^2+1);