/*
System (U^n, V^n), (U^n-1, V^n-1), (F^n-1, F^n)
> (-(1 / k)M^n + (-1/4)(c^2)kA^n)U^n = (-(1 / k)M^n + (1/4)(c^2)kA^n)U^n-1 - M^nV^n-1 + (-1/4)kF^n-1 + (-1/4)kF^n
> M^nV^n = (-1/2)(c^2)kA^nU^n + (-1/2)(c^2)kA^nU^n-1 + M^nV^n-1 + (1/2)kF^n-1 + (1/2)kF^n
*/
const int dim = 2;
using namespace dealii;
int