We use lumping for the nonlinearity, thus we only have diagonal entries

Take the stiffnessmatrix returned by the time stepping scheme; in
particular, this includes a mass term.

Drop members a, V_0, K
Move a into coefficientProduct
Move V_0 into V_m

Add comments that show what we're computing

Also, do a 1-6-0 TNNMG with (six) V-3-3 cycles

Do not re-create overallSolver for every timestep