Hi all, hope you can help.

I have seen examples similar to my problem, for example the Double Pendulum.

For the Double Pendulum, in the Evolution Tab, the last two ODEs are given to be equal to a function (Attachment 1). And the functions are defined in the Custom tab (Attachment 2).

Due to the complicated non-linearity of the coupled simultaneous ODEs whichI am trying to programme, I am hoping to find a way to define all the derivatives in the Evolution Tab without defining a function (Attachment 3), and later writing out the equation of motion to define the system (Attachment 4). Attachment 4 is my attempt to do so, but I tried doing so in the Fixed Varaibles tab.
Right now it is not working, but it could be simply because the system is too complicated or they could be some mistakes in the equation.

But I would like to ask if what I am attempting, could be done. Perhaps there are example out there which I am no aware of which could help me.

Attachment 5 is EJS file.

... sorry, I actually have more to write right now, but I have to go...

Hope you can help. And thanks in advanced.