Nonlinear ODE problem

[ML_7720463]

I am using Mathcad Prime Release 9.0 and Datecode9.0.0.0

Trying to use basic ODE solvers like rkfixed within a solve block. My goal is to solve a pair of nonlinear ODEs (intial value problem) which are not linear in the highest derivative term, using state space if possible. I need to use the iterative solver block because reducing the ODEs to standard form is quite difficult. the odesolve function cannot handle these equations. Are the basic solvers usable in a solve block for this type of problem? If so, an example sheet would be very helpful, the documentation and forums have not been enough. I have begun trying to solve the simple spring/mass system this way, before tackling the full equations, but not yet successful.

Here are the errors that I faced
Variable undefined. Unable to form derivative matrix (odesolve).

[VladimirN]

Please attach your worksheet to the message.

[ML_7720463]

Attached is the simple sheet for spring/mass system.  I have also tried rkfixed solver with similar results.

[LucMeekes]

As far as I know you need to use the standard solvers (rkfixed, AdamsBDF etc,) stand alone, that is NOT in a solve block.

Success!
Luc

[ML_7720463 · Accepted solution]

OK, I will stop trying to make that approach work and just write a program with a solve block and my own integration routine.  Knowing when to move on is just about as valuable as getting the answer.

[Werner_E]

Would this help: