Extended models

Our results indicate that PCG(MG(GS+Cos)) is most effective followed by

PCG(MG(GS)). They are not sensitive to a and deterioration with smaller

h is slow. However, we have not come up with an efficient implementation

for these two methods. Besides, PCG(MG(J+Cos)) shows a degradation over

PCG(MG(GS+Cos)), similar to that of the ordinary GS over Jacobi.