FSP

Preconditioner designed to map onto PETSc's PCFieldSplit.

Overview

The FieldSplitPreconditioner allows for custom preconditioning for each nonlinear variable in the numerical system. One or more variables may be targeted in a subsolve that will only consider part of the numerical system. The preconditioning defined for these subsolves is used for the relevant block(s) in the global numerical system.

A FSP may for example be used for block-diagonal preconditioning by setting full=false and no off-diagonal variable couplings. Numerical systems considering only a single variable are then preconditioned individually. This is the default preconditioner for the PJFNK solves. See the Executioner documentation for more information on the default preconditioner.

More information about field split preconditioning may be found in the PETSc manual.

Example input syntax

In this example, the preconditioning is performed by solving individual problems for each variables, as described in the comments in the snippet. The solution for these subsolves is used to perform the Schur decomposition preconditioning of the main numerical system.

[Preconditioning]
  active = 'FSP'

  [./FSP]
    type = FSP
    # It is the starting point of splitting
    topsplit = 'uv' # 'uv' should match the following block name
    [./uv]
      splitting = 'u v' # 'u' and 'v' are the names of subsolvers
      # Generally speaking, there are four types of splitting we could choose
      # <additive,multiplicative,symmetric_multiplicative,schur>
      splitting_type = additive
      # An approximate solution to the original system
      # | A_uu  A_uv | | u | _ |f_u|
      # |  0    A_vv | | v | - |f_v|
      #  is obtained by solving the following subsystems
      #  A_uu u = f_u and A_vv v = f_v
      # If splitting type is specified as schur, we may also want to set more options to
      # control how schur works using PETSc options
      # petsc_options_iname = '-pc_fieldsplit_schur_fact_type -pc_fieldsplit_schur_precondition'
      # petsc_options_value = 'full selfp'
    [../]
    [./u]
      vars = 'u'
      # PETSc options for this subsolver
      # A prefix will be applied, so just put the options for this subsolver only
      petsc_options_iname = '-pc_type -ksp_type'
      petsc_options_value = '     hypre preonly'
    [../]
    [./v]
      vars = 'v'
      # PETSc options for this subsolver
      petsc_options_iname = '-pc_type -ksp_type'
      petsc_options_value = '     hypre  preonly'
    [../]
  [../]
[]

An example of setting the "off_diag_row" and "off_diag_column" parameters to create a custom coupling matrix may be found in the PBP documentation.

Input Parameters

topsplitEntrance to splits, the top split will specify how splits will go.
C++ Type:std::vector<std::string>
Controllable:No
Description:Entrance to splits, the top split will specify how splits will go.

Required Parameters

fullTrueSet to true if you want the full set of couplings between variables simply for convenience so you don't have to set every off_diag_row and off_diag_column combination.
Default:True
C++ Type:bool
Controllable:No
Description:Set to true if you want the full set of couplings between variables simply for convenience so you don't have to set every off_diag_row and off_diag_column combination.
ksp_normunpreconditionedSets the norm that is used for convergence testing
Default:unpreconditioned
C++ Type:MooseEnum
Options:none, preconditioned, unpreconditioned, natural, default
Controllable:No
Description:Sets the norm that is used for convergence testing
off_diag_columnThe variable names for the off-diagonal columns you want to add into the matrix; they will be associated with an off-diagonal row from the same position in off_diag_row.
C++ Type:std::vector<NonlinearVariableName>
Controllable:No
Description:The variable names for the off-diagonal columns you want to add into the matrix; they will be associated with an off-diagonal row from the same position in off_diag_row.
off_diag_rowThe variable names for the off-diagonal rows you want to add into the matrix; they will be associated with an off-diagonal column from the same position in off_diag_column.
C++ Type:std::vector<NonlinearVariableName>
Controllable:No
Description:The variable names for the off-diagonal rows you want to add into the matrix; they will be associated with an off-diagonal column from the same position in off_diag_column.
pc_sidedefaultPreconditioning side
Default:default
C++ Type:MooseEnum
Options:left, right, symmetric, default
Controllable:No
Description:Preconditioning side

Optional Parameters

control_tagsAdds user-defined labels for accessing object parameters via control logic.
C++ Type:std::vector<std::string>
Controllable:No
Description:Adds user-defined labels for accessing object parameters via control logic.
enableTrueSet the enabled status of the MooseObject.
Default:True
C++ Type:bool
Controllable:No
Description:Set the enabled status of the MooseObject.

Advanced Parameters

mffd_typewpSpecifies the finite differencing type for Jacobian-free solve types. Note that the default is wp (for Walker and Pernice).
Default:wp
C++ Type:MooseEnum
Options:wp, ds
Controllable:No
Description:Specifies the finite differencing type for Jacobian-free solve types. Note that the default is wp (for Walker and Pernice).
petsc_optionsSingleton PETSc options
C++ Type:MultiMooseEnum
Options:-dm_moose_print_embedding, -dm_view, -ksp_converged_reason, -ksp_gmres_modifiedgramschmidt, -ksp_monitor, -ksp_monitor_snes_lg-snes_ksp_ew, -ksp_snes_ew, -snes_converged_reason, -snes_ksp, -snes_ksp_ew, -snes_linesearch_monitor, -snes_mf, -snes_mf_operator, -snes_monitor, -snes_test_display, -snes_view
Controllable:No
Description:Singleton PETSc options
petsc_options_inameNames of PETSc name/value pairs
C++ Type:MultiMooseEnum
Options:-ksp_atol, -ksp_gmres_restart, -ksp_max_it, -ksp_pc_side, -ksp_rtol, -ksp_type, -mat_fd_coloring_err, -mat_fd_type, -mat_mffd_type, -pc_asm_overlap, -pc_factor_levels, -pc_factor_mat_ordering_type, -pc_hypre_boomeramg_grid_sweeps_all, -pc_hypre_boomeramg_max_iter, -pc_hypre_boomeramg_strong_threshold, -pc_hypre_type, -pc_type, -snes_atol, -snes_linesearch_type, -snes_ls, -snes_max_it, -snes_rtol, -snes_divergence_tolerance, -snes_type, -sub_ksp_type, -sub_pc_type
Controllable:No
Description:Names of PETSc name/value pairs
petsc_options_valueValues of PETSc name/value pairs (must correspond with "petsc_options_iname"
C++ Type:std::vector<std::string>
Controllable:No
Description:Values of PETSc name/value pairs (must correspond with "petsc_options_iname"
solve_typePJFNK: Preconditioned Jacobian-Free Newton Krylov JFNK: Jacobian-Free Newton Krylov NEWTON: Full Newton Solve FD: Use finite differences to compute Jacobian LINEAR: Solving a linear problem
C++ Type:MooseEnum
Options:PJFNK, JFNK, NEWTON, FD, LINEAR
Controllable:No
Description:PJFNK: Preconditioned Jacobian-Free Newton Krylov JFNK: Jacobian-Free Newton Krylov NEWTON: Full Newton Solve FD: Use finite differences to compute Jacobian LINEAR: Solving a linear problem

Petsc Parameters

(../moose/test/tests/preconditioners/fsp/fsp_test.i)

[Mesh]
  [./square]
    type = GeneratedMeshGenerator
    nx = 2
    ny = 2
    dim = 2
  [../]
[]

[Variables]
  active = 'u v'

  [./u]
    order = FIRST
    family = LAGRANGE
  [../]

  [./v]
    order = FIRST
    family = LAGRANGE
  [../]
[]

[Kernels]
  active = 'diff_u conv_v diff_v'

  [./diff_u]
    type = Diffusion
    variable = u
  [../]

  [./conv_v]
    type = CoupledForce
    variable = v
    v = u
  [../]

  [./diff_v]
    type = Diffusion
    variable = v
  [../]
[]

[BCs]
  active = 'left_u right_u left_v'

  [./left_u]
    type = DirichletBC
    variable = u
    boundary = 3
    value = 0
  [../]

  [./right_u]
    type = DirichletBC
    variable = u
    boundary = 1
    value = 100
  [../]

  [./left_v]
    type = DirichletBC
    variable = v
    boundary = 3
    value = 0
  [../]

  [./right_v]
    type = DirichletBC
    variable = v
    boundary = 1
    value = 0
  [../]
[]

[Executioner]
  type = Steady

  # This is setup automatically in MOOSE (SetupPBPAction.C)
  # petsc_options = '-snes_mf_operator'
  # petsc_options_iname = '-pc_type'
  # petsc_options_value =  'asm'
[]

[Preconditioning]
  active = 'FSP'

  [./FSP]
    type = FSP
    # It is the starting point of splitting
    topsplit = 'uv' # 'uv' should match the following block name
    [./uv]
      splitting = 'u v' # 'u' and 'v' are the names of subsolvers
      # Generally speaking, there are four types of splitting we could choose
      # <additive,multiplicative,symmetric_multiplicative,schur>
      splitting_type  = additive
      # An approximate solution to the original system
      # | A_uu  A_uv | | u | _ |f_u|
      # |  0    A_vv | | v | - |f_v|
      #  is obtained by solving the following subsystems
      #  A_uu u = f_u and A_vv v = f_v
      # If splitting type is specified as schur, we may also want to set more options to
      # control how schur works using PETSc options
      # petsc_options_iname = '-pc_fieldsplit_schur_fact_type -pc_fieldsplit_schur_precondition'
      # petsc_options_value = 'full selfp'
    [../]
    [./u]
      vars = 'u'
      # PETSc options for this subsolver
      # A prefix will be applied, so just put the options for this subsolver only
      petsc_options_iname = '-pc_type -ksp_type'
      petsc_options_value = '     hypre preonly'
    [../]
    [./v]
      vars = 'v'
      # PETSc options for this subsolver
      petsc_options_iname = '-pc_type -ksp_type'
      petsc_options_value = '     hypre  preonly'
    [../]
  [../]
[]

[Outputs]
  file_base = out
  exodus = true
[]