How can I choose the function U , where U(0)=0 and U˙ is positive definite for the system: <mov

Charity Daniels

Charity Daniels

Answered question

2022-05-24

How can I choose the function U , where U(0)=0 and U˙ is positive definite for the system:
x ˙ = y + x y 2
y ˙ = x + y x 2
Because I want to show that the zero solution of the given system is unstable.

Answer & Explanation

Bettoldi1l

Bettoldi1l

Beginner2022-05-25Added 7 answers

You'll get instability more easily by using the symmetry of the ODE. Namely, let z = z ( t ) (scalar function) be the solution of z = z + z 3 with z ( 0 ) = ϵ. Clearly, z increases with time and tends to infinity. Since ( z ( t ) , z ( t ) ) is a trajectory of the given system with initial point ( ϵ , ϵ ), it follows that ( 0 , 0 ) is unstable.

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