Help on running function in Runge-Kutta

Hello I'm having trouble running a pde in runge-kutta 4

Ive come to conclusion that my U-vector and function are not type correctly. Any help in debugging and running the program would be much appreciated.

I'm trying to run a Burgers equation through RK4 to get solutions. I'm skeptical with my U-vector. I set my boundary conditions for U(1) and U(n-1) I'm trying to run U along with all of the "f" function to get my numerical solutions I made my function in matrix for that way it would be easier for matlab to process however I problaly messed up here.