So we're trying to solve a set of differential equations (that are non linear) that have no algebraic solution that is quite large. When we try and use NDSolve Mathematica attempts to evaluate the code but it gets nowhere and eventually we have to abort the evaluation. When we simplify the set of equations we get the message:
"NDSolve::ntdvdae: Cannot solve to find an explicit formula for the derivatives. NDSolve will try solving the system as differential-algebraic equations."
So we're guessing that NDSolve is attempting to somehow massage the equations into a more manageable form before it gives up and just starts numerically solving it. The problem for us is that the more complicated set of equations we have is so large that mathematica does not seem to realise that it cannot massage them into a more manageable form... thus it never gets to the point where it uses the solving method that actually works.
So I guess what we were wondering is how can we force mathematica to use the method that works straight away?
Thanks and sorry for the rambling message.