1. Add alpha to control over-relaxation, but
   it seems that the number is very sensitive if alpha > 1.0

2. Resolve the problem of checking integral.
Merge pull request #2 from meteorologytoday/Overrelaxation

Finish

1. Add alpha to control over-relaxation, but it seems that the number is very sensitive if alpha > 1.0
2. Resolve the problem of checking integral.