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  1. M

    Phase portrait

    How can I construct the phase portrait(with Mathematica) of the following system? \dot{x}(t)=y(t) \dot{y}(t)=-x^3(t)+4x(t)y(t)
  2. M

    System PDEs - Comsol

    Hello! I have to solve a system of PDEs with Comsol and do not know where to start ... This is the system: &u_{,x}+v_{,y}=k y+h x\ \ \ &in\ \mathcal{A} v_{,x}-u_{,y}=k x-h y\ \ \ &in\ \mathcal{A} u n_x+v n_y=0\ \ \ &on\ \partial\mathcal{A} \mathcal{A}\ in\...
  3. M

    Vector Potential

    Hello! Can you tell me the sufficient condition for the existence of the vector potential? Thank you very much!