[petsc-users] Question on PETSc solver iteration and convergence

[Danyang Su]

Hi All,

I implement KSP solver in a Newton iteration. The convergence parameters 
are: rtol 1.0E-8, abstol 1.0E-50, dtol 1.0E5, maxits 1000.

Does the following convergence monitoring make sense? I thought the 
solver should stop before iteration 36, but it stops at iteration 70.

  0 KSP preconditioned resid norm 4.208619583781e-002 true resid norm 
2.227983625699e-005 ||r(i)||/||b|| 1.000000000000e+000
  1 KSP preconditioned resid norm 6.403275610900e-003 true resid norm 
2.795175726580e-007 ||r(i)||/||b|| 1.254576422528e-002
  2 KSP preconditioned resid norm 7.416300263102e-004 true resid norm 
3.382118379502e-010 ||r(i)||/||b|| 1.518017610404e-005
  3 KSP preconditioned resid norm 6.144409100696e-005 true resid norm 
1.260466100377e-009 ||r(i)||/||b|| 5.657429820568e-005
  4 KSP preconditioned resid norm 4.990158094666e-005 true resid norm 
3.632496726225e-008 ||r(i)||/||b|| 1.630396509349e-003
  5 KSP preconditioned resid norm 2.743769015994e-005 true resid norm 
1.101666758939e-009 ||r(i)||/||b|| 4.944680680017e-005
  6 KSP preconditioned resid norm 4.269805798759e-006 true resid norm 
7.915494521121e-011 ||r(i)||/||b|| 3.552761532813e-006
  7 KSP preconditioned resid norm 1.632413041808e-006 true resid norm 
1.163794439302e-009 ||r(i)||/||b|| 5.223532282187e-005
  8 KSP preconditioned resid norm 8.010590587547e-007 true resid norm 
1.246839309256e-011 ||r(i)||/||b|| 5.596267831030e-007
  9 KSP preconditioned resid norm 4.794695759395e-007 true resid norm 
3.155943984006e-012 ||r(i)||/||b|| 1.416502324166e-007
 10 KSP preconditioned resid norm 4.500033799628e-007 true resid norm 
4.554787575528e-011 ||r(i)||/||b|| 2.044354151884e-006
...
 36 KSP preconditioned resid norm 2.752424650444e-009 true resid norm 
2.990835953592e-016 ||r(i)||/||b|| 1.342395841286e-011
...
 51 KSP preconditioned resid norm 5.761764412500e-010 true resid norm 
2.557370618510e-016 ||r(i)||/||b|| 1.147840849911e-011
...
 69 KSP preconditioned resid norm 4.324655127362e-010 true resid norm 
1.982933485715e-014 ||r(i)||/||b|| 8.900125938281e-010
 70 KSP preconditioned resid norm 3.923752626311e-010 true resid norm 
1.065002491928e-015 ||r(i)||/||b|| 4.780118128535e-011

Thanks,

Danyang