Documentation for PISM, the Parallel Ice Sheet Model

Differences

This shows you the differences between two versions of the page.

Link to this comparison view

Both sides previous revision Previous revision
kspdiverged [2014/07/11 12:58]
Ed Bueler clarified that it can be either of the "effective viscosity not converged" or "KSPSolve() ... diverged" cases, and integrated Jed's comment in reasonable way
kspdiverged [2014/10/10 16:36] (current)
Constantine Khroulev
Line 33: Line 33:
   - The failure may be resolved by adding options. ​ Specifically,​ an iceberg may have been created, for which the stress balance is ill-posed (i.e. not invertible even in theory). ​ You should use ''​-kill_icebergs''​. ​ More general advice is to use ''​-pik'',​ which implies ''​-kill_icebergs'',​ for most runs.   - The failure may be resolved by adding options. ​ Specifically,​ an iceberg may have been created, for which the stress balance is ill-posed (i.e. not invertible even in theory). ​ You should use ''​-kill_icebergs''​. ​ More general advice is to use ''​-pik'',​ which implies ''​-kill_icebergs'',​ for most runs.
   - The problem occurs most often with steep bed topography. ​ The special problematic case may be nunataks, i.e. steep mountains poking up through the ice sheet. ​ Consider using a smoother interpolation scheme for the bed topography, if that is justified given the bed elevation data you have.   - The problem occurs most often with steep bed topography. ​ The special problematic case may be nunataks, i.e. steep mountains poking up through the ice sheet. ​ Consider using a smoother interpolation scheme for the bed topography, if that is justified given the bed elevation data you have.
-  - In the "''​KSPSolve() reports '​diverged'''"​ case you may observe that the system is solvable with stronger PETSc linear solver options. ​ Specifically,​ you can add these "​direct subdomain solves"​ options to your PISM run: <​code>​ +  - In the "''​KSPSolve() reports '​diverged'''"​ case you may observe that the system is solvable with stronger PETSc linear solver options. ​ Specifically,​ you can add these "​direct subdomain solves"​ options to your PISM run: 
--ksp_type ​gmres -ksp_norm_type ​unpreconditioned -ksp_pc_side ​right -pc_type ​asm -sub_pc_type ​lu +<​code>​ 
-</​code> ​ The run will likely be about a factor of two slower but it will probably not generate the errors. ​ For more discussion of PETSc solver options which may help with performance and robustness of PISM runs, see [[petscoptions|the page on PETSc solver options]].+-ssafd_ksp_type ​gmres -ssafd_ksp_norm_type ​unpreconditioned -ssafd_ksp_pc_side ​right -ssafd_pc_type ​asm -ssafd_sub_pc_type ​lu 
 +</​code>​ 
 + 
 +The run will likely be about a factor of two slower but it will probably not generate the errors. ​ For more discussion of PETSc solver options which may help with performance and robustness of PISM runs, see [[petscoptions|the page on PETSc solver options]].
  
  
kspdiverged.txt · Last modified: 2014/10/10 16:36 by Constantine Khroulev
© 2016 by PISM | webmaster