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Hi PF
The following ODE
$$\ddot x + x  x^3 = 0\\
x(0)=0,\,\,\,\dot x(0) = \frac {1}{ \sqrt 2}$$
is solve exactly with ##\tanh (t/\sqrt 2)##. However, when I try to solve this with MATLAB ode45 (ode23t looks identical) or Mathematica NDSolve I get an oscillatory numerical solution (see attached).
Any idea what's going wrong?
The following ODE
$$\ddot x + x  x^3 = 0\\
x(0)=0,\,\,\,\dot x(0) = \frac {1}{ \sqrt 2}$$
is solve exactly with ##\tanh (t/\sqrt 2)##. However, when I try to solve this with MATLAB ode45 (ode23t looks identical) or Mathematica NDSolve I get an oscillatory numerical solution (see attached).
Any idea what's going wrong?
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