a question about bvp4c

Dear friends;

I wanna solve an optimal control problem with free-final-time by means of bvp4c; so I have to use a function like:

function res = bc(ya,yb)
res = [ ya(1) - 1; ya(2) - 2; yb(1) - 3; yb(4); yb(3)*yb(2)-0.5*yb(4)^2];

Now, I have 2 questions:

1. The equation which should be placed in the last array of res matrix is too long, so can I save it in another parameter and then use that parameter in matrix?

2. This equation is a function of some other parameters (q1, q2, dq1, dq2); so should I replace them by yb(1)-yb(4)? And how? (Because as I mentioned my equation is too large).

Regards