ODE vs DAE (from Val Ochkov)

[AlanStevens]

Why does the third solve block not work?

(Mathcad Prime 9)

[LucMeekes]

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

[Werner_E]

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.

[AlanStevens · Accepted solution]

Val sends his thanks to all, and notes that he has solved the problem using Mathematica: