how can i write this?

With all the letters available, why are we using "C" as the name of separate variables?

You define C1, C2, ... C5 each as a two value vector.  At that point, C is a six valued vector; the first position (C0) has nothing in it (default 0) and the other five positions each have a vector with two numbers.

Then you try to create a matrix with name C (again!).  This matrix is supposed to be a 4 X 4 matrix (from 0 to 3), and it looks like you're trying to put a vector in each position along the diagonal with two values in it.

Might work if you change the name of the matrix!