RKfixed Help

[crusk]

Hey guys, I am attempting to solve a complex problem with rkfixed.  At the bottom of my sheet is where you will find the function.  I have my ODE defined with the variable "D", and when I run rkfixed it returns "this function cannot be used here".  I have been researching for hours with no luck to find the reason.  Can someone please help?

[Werner_E]

First error i spot is at page 2 - a unit mismatch

Not sure if it it is used later and has anything to with the solve block, but I would not go any further without fixing that problem.

Second error I spotted is the use of the vector cross product instead of a normal multiplication

After fixing that the solve block works, but stops with the error "This value must be real". That error is not traceable. No clue what the reason could be. Maybe you'll have to check your model for inconsistencies.

[Tmetcalf]

Good day Clint,

Welcome to PTC Community and I hope Werner Exinger‌'s answer was helpful.

If so, would you please make it as correct - this will let other readers know about this solution.

Thank you for participating.

Best,

Toby

[-MFra-]

Hi Clint Rusk,

by the following expression on, you have to make corrections. The coefficients can not be dimensionless, as is evident.

You can not use the units just wherever you like ..