solving a differential equation coupling together in matrix and vector form with ode45

I have two problem:

1) I used two functions for solving a set of equation not in matrix or vector form but like

[x(2);3+x(4)+x(3);x(4);....................]

then [t,x] = ode45(@(t,x) lili(t,x),tspan,x0);

now I need the vector of dx=[x(2) x(4) x(6)]

but it doesnt return this vector.

2) i want to solve equation like this D2y=d2x+cross(m,n)

its clear cross product is in matrix form

how could i solve matrix form of differential equation?

especially initial values is a vector