compress row of MapMatrix into vector from map after assembling. Note: woking for ILU but cannot pass regreesion test because       el() and set() operations are not valid after compress.
compress row of MapMatrix into vector from map after assembling.
Note: woking for ILU but cannot pass regreesion test because
      el() and set() operations are not valid after compress.

QiaoLei-88/NSolver,QiaoLei-88/NSolver