Thank you. This was the information I needed. However, I'm just curious: in general, if I have a system of three second-order differential equations (and initial conditions) in dsys:={}, and enter dsol:=dsolve(dsys, numeric, it returns

proc...rk4...end_proc

or something like that. If I type something wrong, it says it couldn't convert it to an explicit first order system, which implies to me that that's what the aformentioned message means. Do you know of a way to display the resulting first order?