ODE vs DAE (from Val Ochkov)

Hi Valery,

The highest derivative of the sought function must be on the LHS of the equation.
Reason: Odesolve uses the/an RK4 algorithm, where the (highest derivative of the) sought function must be expressed as an explicit definition.

Success!
Luc

According to the help "The ODE must be linear in their highest derivative term" which is not the case when the derivative is used as argument of arctan.