[petsc-users] Lowly convergenced rate of GMRES

[李瑞]

Dear professor or engineer:
   I use GMRES method to solve a linear Non-Hermite equation.To improve the convergenced rate of GMRES method in limited steps,I have tried serval ways i can do.My makefile is written such following content:

>>...
>> -ksp_monitor -ksp_max_it 500 \ksp_type gmres \
>> -ksp_gmres_restart 90  -ksp_atol 1.e-6 \
>> -ksp_rtol 1.e-9  -ksp_pc_side right \
>> -pc_type asm  -pc_asm_type restrict  -pc_asm_overlap 2 \
>> -sub_ksp_type preonly -sub_pc_type lu 

The result is always not pleasure.
    1 KSP Residual norm 4.436461190051e+04 
    2 KSP Residual norm 9.773182866331e+03 
    3 KSP Residual norm 8.432841532618e+03 
    4 KSP Residual norm 7.642491240521e+03
          ...... 
  497 KSP Residual norm 5.345439499920e+02 
  498 KSP Residual norm 5.269741944074e+02 
  499 KSP Residual norm 5.197171806884e+02 
  500 KSP Residual norm 5.127519507363e+02

Could you provide some ideas to increase the convergenced rate of this type of method?Thanks！