Residual

This post-processor computes the nonlinear residual norm. The parameter "residual_type" may have one of the following values:

FINAL: The final norm, obtained by NonlinearSystemBase::finalNonlinearResidual()
INITIAL: The post-SMO initial residual norm, obtained by NonlinearSystemBase::preSMOResidual(). For the definition of pre- vs. post-SMO residual, see NonlinearSystem.
PRE_SMO: The pre-SMO initial residual norm, obtained by NonlinearSystemBase::initialResidual()
CURRENT: The current norm, obtained directly from the PETSc SNES object. Note that the norm obtained from PETSc does not always provide the latest value; for example, executing on NONLINEAR yields 0.
COMPUTE: The norm is actually computed at the time of execution.

A common use of this post-processor is to assess the convergence of iterative solve loops using PostprocessorConvergence or MultiPostprocessorConvergence, for example. For this to work as expected, the execute_on parameter of the post-processor must include values that trigger execution before the desired check. The following table lists general recommendations for which execute_on flags to include for each type of convergence check. See SetupInterface for details on different execution points.

Convergence Check	Recommended `residual_type`	Recommended `execute_on`
Nonlinear	`CURRENT`	`NONLINEAR_CONVERGENCE`
MultiApp fixed point, executing MultiApps only on `TIMESTEP_BEGIN`	`COMPUTE`	`TIMESTEP_BEGIN`
MultiApp fixed point, executing MultiApps only on `TIMESTEP_END`	`COMPUTE`	`MULTIAPP_FIXED_POINT_CONVERGENCE`
MultiApp fixed point, executing MultiApps only on both `TIMESTEP_BEGIN` and `TIMESTEP_END`	`COMPUTE`	Use two `Residual` objects, one with `execute_on = MULTIAPP_FIXED_POINT_CONVERGENCE` for the `TIMESTEP_END` MultiApps and one with `execute_on = TIMESTEP_BEGIN` for the `TIMESTEP_BEGIN` MultiApps. Then combine both with the `&` operator in ParsedConvergence
Multi-system fixed point	`COMPUTE`	`MULTISYSTEM_FIXED_POINT_CONVERGENCE`

More information about residuals and their use in Newton's method may be found in NonlinearSystem.

The residual may be split by variables using the VariableResidual postprocessor.

Example input syntax

In this example, u is the solution of a diffusion problem. A predictor time integrating scheme is used and the Residual postprocessor reports the residual.

[Postprocessors<<<{"href": "../../syntax/Postprocessors/index.html"}>>>]
  [final_residual]
    type = Residual<<<{"description": "Report the non-linear residual.", "href": "Residual.html"}>>>
    residual_type<<<{"description": "Type of residual to be reported."}>>> = FINAL
  []
  [initial_residual]
    type = Residual<<<{"description": "Report the non-linear residual.", "href": "Residual.html"}>>>
    residual_type<<<{"description": "Type of residual to be reported."}>>> = INITIAL
  []
[]

Input Parameters

residual_typeFINALType of residual to be reported.
Default:FINAL
C++ Type:MooseEnum
Options:FINAL, INITIAL_BEFORE_PRESET, INITIAL_AFTER_PRESET, PRE_SMO, INITIAL, CURRENT, COMPUTE
Controllable:No
Description:Type of residual to be reported.

Optional Parameters

allow_duplicate_execution_on_initialFalseIn the case where this UserObject is depended upon by an initial condition, allow it to be executed twice during the initial setup (once before the IC and again after mesh adaptivity (if applicable).
Default:False
C++ Type:bool
Controllable:No
Description:In the case where this UserObject is depended upon by an initial condition, allow it to be executed twice during the initial setup (once before the IC and again after mesh adaptivity (if applicable).
execute_onTIMESTEP_ENDThe list of flag(s) indicating when this object should be executed. For a description of each flag, see https://mooseframework.inl.gov/source/interfaces/SetupInterface.html.
Default:TIMESTEP_END
C++ Type:ExecFlagEnum
Options:XFEM_MARK, FORWARD, ADJOINT, HOMOGENEOUS_FORWARD, ADJOINT_TIMESTEP_BEGIN, ADJOINT_TIMESTEP_END, NONE, INITIAL, LINEAR, LINEAR_CONVERGENCE, NONLINEAR, NONLINEAR_CONVERGENCE, POSTCHECK, TIMESTEP_END, TIMESTEP_BEGIN, MULTIAPP_FIXED_POINT_END, MULTIAPP_FIXED_POINT_BEGIN, MULTIAPP_FIXED_POINT_CONVERGENCE, MULTISYSTEM_FIXED_POINT_CONVERGENCE, FINAL, CUSTOM, TRANSFER
Controllable:No
Description:The list of flag(s) indicating when this object should be executed. For a description of each flag, see https://mooseframework.inl.gov/source/interfaces/SetupInterface.html.
execution_order_group0Execution order groups are executed in increasing order (e.g., the lowest number is executed first). Note that negative group numbers may be used to execute groups before the default (0) group. Please refer to the user object documentation for ordering of user object execution within a group.
Default:0
C++ Type:int
Controllable:No
Description:Execution order groups are executed in increasing order (e.g., the lowest number is executed first). Note that negative group numbers may be used to execute groups before the default (0) group. Please refer to the user object documentation for ordering of user object execution within a group.
force_postauxFalseForces the UserObject to be executed in POSTAUX
Default:False
C++ Type:bool
Controllable:No
Description:Forces the UserObject to be executed in POSTAUX
force_preauxFalseForces the UserObject to be executed in PREAUX
Default:False
C++ Type:bool
Controllable:No
Description:Forces the UserObject to be executed in PREAUX
force_preicFalseForces the UserObject to be executed in PREIC during initial setup
Default:False
C++ Type:bool
Controllable:No
Description:Forces the UserObject to be executed in PREIC during initial setup

Execution Scheduling 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:Yes
Description:Set the enabled status of the MooseObject.
outputsVector of output names where you would like to restrict the output of variables(s) associated with this object
C++ Type:std::vector<OutputName>
Controllable:No
Description:Vector of output names where you would like to restrict the output of variables(s) associated with this object
use_displaced_meshFalseWhether or not this object should use the displaced mesh for computation. Note that in the case this is true but no displacements are provided in the Mesh block the undisplaced mesh will still be used.
Default:False
C++ Type:bool
Controllable:No
Description:Whether or not this object should use the displaced mesh for computation. Note that in the case this is true but no displacements are provided in the Mesh block the undisplaced mesh will still be used.

Advanced Parameters

prop_getter_suffixAn optional suffix parameter that can be appended to any attempt to retrieve/get material properties. The suffix will be prepended with a '_' character.
C++ Type:MaterialPropertyName
Unit:(no unit assumed)
Controllable:No
Description:An optional suffix parameter that can be appended to any attempt to retrieve/get material properties. The suffix will be prepended with a '_' character.
use_interpolated_stateFalseFor the old and older state use projected material properties interpolated at the quadrature points. To set up projection use the ProjectedStatefulMaterialStorageAction.
Default:False
C++ Type:bool
Controllable:No
Description:For the old and older state use projected material properties interpolated at the quadrature points. To set up projection use the ProjectedStatefulMaterialStorageAction.

Material Property Retrieval Parameters

Input Files

(test/tests/predictors/simple/predictor_skip_test.i)
(test/tests/multisystem/picard/nonlinearfe_nonlinearfe/multi_system.i)
(test/tests/convergence/postprocessor_convergence/multiapp_fp.i)
(test/tests/predictors/simple/predictor_test.i)
(test/tests/postprocessors/residual/current_residual.i)
(test/tests/postprocessors/residual/eigen_problem.i)
(modules/contact/test/tests/glued/glued_contact_mechanical_constraint_test.i)
(test/tests/predictors/simple/predictor_test_pre_smo.i)
(test/tests/constraints/equal_value_boundary_constraint/equal_value_boundary_constraint_test.i)
(test/tests/predictors/simple/predictor_test_skip_after_failed_tstep.i)
(test/tests/predictors/simple/predictor_skip_old_test.i)

(test/tests/predictors/simple/predictor_test.i)

# The purpose of this test is to test the simple predictor.  This is a very
# small, monotonically loaded block of material.  If things are working right,
# the predictor should come very close to exactly nailing the solution on steps
# after the first step.

# The main thing to check here is that when the predictor is applied in the
# second step, the initial residual is almost zero.

[Mesh]
  type = GeneratedMesh
  dim = 2
  xmin = 0
  xmax = 1
  ymin = 0
  ymax = 1
  nx = 3
  ny = 3
[]

[Functions]
  [ramp1]
    type = ParsedFunction
    expression = 't'
  []
[]

[Variables]
  [u]
    order = FIRST
    family = LAGRANGE
  []
[]

[Kernels]
  [diff_u]
    type = Diffusion
    variable = u
  []
[]

[BCs]
  [bot]
    type = DirichletBC
    variable = u
    boundary = bottom
    value = 0.0
  []
  [ss2_x]
    type = FunctionDirichletBC
    variable = u
    boundary = top
    function = ramp1
  []
[]

[Executioner]
  type = Transient
  solve_type = 'PJFNK'

  nl_max_its = 15
  nl_rel_tol = 1e-14
  nl_abs_tol = 1e-14

  start_time = 0.0
  dt = 0.5
  end_time = 1.0

  [Predictor]
    type = SimplePredictor
    scale = 1.0
  []
[]

[Postprocessors]
  [final_residual]
    type = Residual
    residual_type = FINAL
  []
  [initial_residual]
    type = Residual
    residual_type = INITIAL
  []
[]

[Outputs]
  csv = true
[]

(test/tests/predictors/simple/predictor_skip_test.i)

# The purpose of this test is to test the simple predictor.  This is a very
# small, monotonically loaded block of material.  If things are working right,
# the predictor should come very close to exactly nailing the solution on steps
# after the first step.

#This test checks to see that the predictor is skipped in the last step.

[Mesh]
  type = GeneratedMesh
  dim = 2
  xmin = 0
  xmax = 1
  ymin = 0
  ymax = 1
  nx = 3
  ny = 3
[]

[Functions]
  [ramp1]
    type = ParsedFunction
    expression = 't'
  []
[]

[Variables]
  [u]
    order = FIRST
    family = LAGRANGE
  []
[]

[Kernels]
  [diff_u]
    type = Diffusion
    variable = u
  []
[]

[BCs]
  [bot]
    type = DirichletBC
    variable = u
    boundary = bottom
    value = 0.0
  []
  [ss2_x]
    type = FunctionDirichletBC
    variable = u
    boundary = top
    function = ramp1
  []
[]

[Executioner]
  type = Transient
  solve_type = 'PJFNK'

  nl_max_its = 15
  nl_rel_tol = 1e-14
  nl_abs_tol = 1e-14

  start_time = 0.0
  dt = 0.5
  end_time = 1.0

  [Predictor]
    type = SimplePredictor
    scale = 1.0
    skip_times = '1.0'
  []
[]

[Postprocessors]
  [final_residual]
    type = Residual
    residual_type = FINAL
  []
  [initial_residual]
    type = Residual
    residual_type = INITIAL
  []
[]

[Outputs]
  csv = true
[]

(test/tests/multisystem/picard/nonlinearfe_nonlinearfe/multi_system.i)

# Solves problem in a multi-system fixed point solve.

!include base.i

[Problem]
  nl_sys_names = 'u_sys v_sys'
[]

[Variables]
  [u]
    solver_sys = u_sys
  []
  [v]
    solver_sys = v_sys
  []
[]

[Postprocessors]
  [res_norm]
    type = Residual
    residual_type = COMPUTE
    execute_on = 'MULTISYSTEM_FIXED_POINT_CONVERGENCE'
  []
[]

[Convergence]
  [u_conv]
    type = DefaultNonlinearConvergence
    nl_abs_tol = 1e-8
    nl_rel_tol = 1e-8
    nl_max_its = 10
  []
  [v_conv]
    type = DefaultNonlinearConvergence
    nl_abs_tol = 1e-8
    nl_rel_tol = 1e-8
    nl_max_its = 10
  []
  [fp_conv]
    type = PostprocessorConvergence
    postprocessor = res_norm
    tolerance = 1e-8
    max_iterations = 10
    verbose = true
  []
[]

[Executioner]
  nonlinear_convergence = 'u_conv v_conv'
  multi_system_fixed_point = true
  multi_system_fixed_point_convergence = fp_conv
[]

[Outputs]
  file_base = multi_system
[]

(test/tests/convergence/postprocessor_convergence/multiapp_fp.i)

!include ../parent.i

[Convergence]
  [fp_conv]
    type = PostprocessorConvergence
    postprocessor = nl_res
    tolerance = 1e-2
    max_iterations = 15
  []
[]

[Postprocessors]
  [nl_res]
    type = Residual
    residual_type = COMPUTE
    execute_on = 'MULTIAPP_FIXED_POINT_CONVERGENCE'
  []
[]

(test/tests/predictors/simple/predictor_test.i)

# The purpose of this test is to test the simple predictor.  This is a very
# small, monotonically loaded block of material.  If things are working right,
# the predictor should come very close to exactly nailing the solution on steps
# after the first step.

# The main thing to check here is that when the predictor is applied in the
# second step, the initial residual is almost zero.

[Mesh]
  type = GeneratedMesh
  dim = 2
  xmin = 0
  xmax = 1
  ymin = 0
  ymax = 1
  nx = 3
  ny = 3
[]

[Functions]
  [ramp1]
    type = ParsedFunction
    expression = 't'
  []
[]

[Variables]
  [u]
    order = FIRST
    family = LAGRANGE
  []
[]

[Kernels]
  [diff_u]
    type = Diffusion
    variable = u
  []
[]

[BCs]
  [bot]
    type = DirichletBC
    variable = u
    boundary = bottom
    value = 0.0
  []
  [ss2_x]
    type = FunctionDirichletBC
    variable = u
    boundary = top
    function = ramp1
  []
[]

[Executioner]
  type = Transient
  solve_type = 'PJFNK'

  nl_max_its = 15
  nl_rel_tol = 1e-14
  nl_abs_tol = 1e-14

  start_time = 0.0
  dt = 0.5
  end_time = 1.0

  [Predictor]
    type = SimplePredictor
    scale = 1.0
  []
[]

[Postprocessors]
  [final_residual]
    type = Residual
    residual_type = FINAL
  []
  [initial_residual]
    type = Residual
    residual_type = INITIAL
  []
[]

[Outputs]
  csv = true
[]

(test/tests/postprocessors/residual/current_residual.i)

[Mesh]
  type = GeneratedMesh
  dim = 2
  nx = 10
  ny = 10
[]

[Variables]
  [u]
  []
[]

[Kernels]
  [diff]
    type = Diffusion
    variable = u
  []
[]

[BCs]
  [left]
    type = DirichletBC
    variable = u
    boundary = left
    value = 0
  []
  [right]
    type = DirichletBC
    variable = u
    boundary = right
    value = 1
  []
[]

[Postprocessors]
  [test_pp]
    type = Residual
    residual_type = CURRENT
    execute_on = 'NONLINEAR_CONVERGENCE'
  []
[]

[Executioner]
  type = Steady
  solve_type = 'PJFNK'
  petsc_options_iname = '-pc_type'
  petsc_options_value = 'hypre'
[]

[Outputs]
  [out]
    type = CSV
    execute_on = 'NONLINEAR'
  []
[]

(test/tests/postprocessors/residual/eigen_problem.i)

# Test problem modified from ../../problems/eigen_problem/eigensolvers/ne.i:
#
# The minimum eigenvalue of this problem is 2*(PI/a)^2;
# Its inverse is 0.5*(a/PI)^2 = 5.0660591821169. Here a is equal to 10.

[Mesh]
  [gen]
    type = GeneratedMeshGenerator
    dim = 2
    xmin = 0
    xmax = 10
    ymin = 0
    ymax = 10
    elem_type = QUAD4
    nx = 8
    ny = 8
  []
[]

[Variables]
  [u]
    order = FIRST
    family = LAGRANGE
  []
[]

[Kernels]
  [diff]
    type = Diffusion
    variable = u
  []
  [rhs]
    type = Reaction
    variable = u
    rate = -1.0
    extra_vector_tags = 'eigen'
  []
[]

[BCs]
  [homogeneous]
    type = DirichletBC
    variable = u
    boundary = '0 1 2 3'
    value = 0
  []
  [eigen]
    type = EigenDirichletBC
    variable = u
    boundary = '0 1 2 3'
  []
[]

[Postprocessors]
  [residual]
    type = Residual
  []
[]

[Executioner]
  type = Eigenvalue
  solve_type = PJFNK
  nl_abs_tol = 1e-4 # This should take a single nonlinear iteration
[]

[Outputs]
  csv = true
  execute_on = 'FINAL'
[]

(modules/contact/test/tests/glued/glued_contact_mechanical_constraint_test.i)

# This is a mechanical constraint (contact formulation) version of glued_contact_mechanical_constraint.i
[Mesh]
  file = glued_contact_test.e
[]

[GlobalParams]
  volumetric_locking_correction = true
  displacements = 'disp_x disp_y disp_z'
[]

[Functions]
  [./up]
    type = PiecewiseLinear
    x = '0 1'
    y = '0 0.5001'
  [../]

  [./lateral]
    type = PiecewiseLinear
    x = '0 1 2 3'
    y = '0 0 1 0'
    scale_factor = 0.5
  [../]
[]

[Variables]
  [./disp_x]
  [../]
  [./disp_y]
  [../]
  [./disp_z]
  [../]
[]

[Kernels]
  [./TensorMechanics]
    use_displaced_mesh = true
  [../]
[]

[Contact]
  [./dummy_name]
    primary = 2
    secondary = 3
    penalty = 1e6
    model = glued
    formulation = kinematic
  [../]
[]

[BCs]

  [./bottom_lateral]
    type = FunctionDirichletBC
    variable = disp_x
    boundary = 1
    function = lateral
  [../]

  [./bottom_up]
    type = FunctionDirichletBC
    variable = disp_y
    boundary = 1
    function = up
  [../]

  [./bottom_out]
    type = DirichletBC
    variable = disp_z
    boundary = 1
    value = 0.0
  [../]

  [./top]
    type = DirichletBC
    variable = disp_y
    boundary = 4
    value = 0.0
  [../]
[]

[Materials]
  [./stiffStuff1]
    type = ComputeIsotropicElasticityTensor
    block = '1'
    youngs_modulus = 1e6
    poissons_ratio = 0.3
  [../]
  [./stiffStuff1_strain]
    type= ComputeFiniteStrain
    block = '1'
  [../]
  [./stiffStuff1_stress]
    type = ComputeFiniteStrainElasticStress
    block = '1'
  [../]

  [./stiffStuff2]
    type = ComputeIsotropicElasticityTensor
    block = '2'
    youngs_modulus = 1e6
    poissons_ratio = 0.3
  [../]
  [./stiffStuff2_strain]
    type= ComputeFiniteStrain
    block = '2'
  [../]
  [./stiffStuff2_stress]
    type = ComputeFiniteStrainElasticStress
    block = '2'
  [../]
[]

[Executioner]
  type = Transient
  solve_type = 'PJFNK'

  #petsc_options_iname = '-pc_type -pc_hypre_type -snes_type -snes_ls -snes_linesearch_type -ksp_gmres_restart'
  #petsc_options_value = 'hypre    boomeramg      ls         basic    basic                    101'
  petsc_options_iname = '-pc_type -ksp_gmres_restart'
  petsc_options_value = 'ilu      101'

  line_search = 'none'

  nl_abs_tol = 1e-8
  nl_rel_tol = 1e-8
  l_tol = 1e-4

  l_max_its = 100
  nl_max_its = 10
  dt = 0.1
  num_steps = 30

  [./Predictor]
    type = SimplePredictor
    scale = 1.0
  [../]
[]

[Postprocessors]
  active = ''
  [./resid]
    type = Residual
  [../]
  [./iters]
    type = NumNonlinearIterations
  [../]
[]

[Outputs]
  file_base = mechanical_constraint_out
  exodus = true
[]

(test/tests/predictors/simple/predictor_test_pre_smo.i)

# The purpose of this test is to test the simple predictor.  This is a very
# small, monotonically loaded block of material.  If things are working right,
# the predictor should come very close to exactly nailing the solution on steps
# after the first step.

# The main thing to check here is that when the predictor is applied in the
# second step, the initial residual is almost zero.

[Mesh]
  type = GeneratedMesh
  dim = 2
  xmin = 0
  xmax = 1
  ymin = 0
  ymax = 1
  nx = 3
  ny = 3
[]

[Functions]
  [ramp1]
    type = ParsedFunction
    expression = 't'
  []
[]

[Variables]
  [u]
    order = FIRST
    family = LAGRANGE
  []
[]

[Kernels]
  [diff_u]
    type = Diffusion
    variable = u
  []
[]

[BCs]
  [bot]
    type = DirichletBC
    variable = u
    boundary = bottom
    value = 0.0
  []
  [ss2_x]
    type = FunctionDirichletBC
    variable = u
    boundary = top
    function = ramp1
  []
[]

[Executioner]
  type = Transient
  solve_type = 'PJFNK'

  nl_max_its = 15
  nl_rel_tol = 1e-14
  nl_abs_tol = 1e-14

  start_time = 0.0
  dt = 0.5
  end_time = 1.0

  [Predictor]
    type = SimplePredictor
    scale = 1.0
  []

  use_pre_SMO_residual = true
[]

[Postprocessors]
  [final_residual]
    type = Residual
    residual_type = FINAL
  []
  [pre_smo_residual]
    type = Residual
    residual_type = PRE_SMO
  []
  [initial_residual]
    type = Residual
    residual_type = INITIAL
  []
[]

[Outputs]
  csv = true
[]

(test/tests/constraints/equal_value_boundary_constraint/equal_value_boundary_constraint_test.i)

[Mesh]
  type = GeneratedMesh
  dim = 2
  nx = 6
  ny = 6
  elem_type = QUAD4
  allow_renumbering = false
[]

[Variables]
  [diffused]
    order = FIRST
    family = LAGRANGE
  []
[]

[Kernels]
  [diff]
    type = Diffusion
    variable = diffused
  []
[]

[Problem]
  error_on_jacobian_nonzero_reallocation = true
[]

[BCs]
  [left]
    type = DirichletBC
    variable = diffused
    preset = false
    boundary = 'left'
    value = 1.0
  []
  [right]
    type = DirichletBC
    variable = diffused
    preset = false
    boundary = 'right'
    value = 0.0
  []
[]

# Constraint System
[Constraints]
  [y_top]
    type = EqualValueBoundaryConstraint
    variable = diffused
    secondary = 'top' # boundary
    penalty = 10e6
  []
[]

[Executioner]
  type = Steady

  solve_type = 'PJFNK'

  petsc_options_iname = ''
  petsc_options_value = ''

  line_search = 'none'
[]

[Postprocessors]
  active = ' '

  [residual]
    type = Residual
  []

  [nl_its]
    type = NumNonlinearIterations
  []

  [lin_its]
    type = NumLinearIterations
  []
[]

[Outputs]
  execute_on = 'timestep_end'
  file_base = out
  exodus = true
[]

(test/tests/predictors/simple/predictor_test_skip_after_failed_tstep.i)

# The purpose of this test is to test the simple predictor.
# The test is adjusted to produce a failed time step.
# The predictor option 'skip_after_failed_timestep' should suppress a prediction
# after the failed time step.

[Mesh]
  type = GeneratedMesh
  dim = 2
  xmin = 0
  xmax = 1
  ymin = 0
  ymax = 1
  nx = 3
  ny = 3
[]

[Functions]
  [ramp1]
    type = PiecewiseLinear
    x = '0      0.5     1'
    y = '0      1       4'
  []
[]

[Variables]
  [u]
    order = FIRST
    family = LAGRANGE
  []
[]

[Kernels]
  [diff_u]
    type = Diffusion
    variable = u
  []
[]

[BCs]
  [bot]
    type = DirichletBC
    variable = u
    boundary = bottom
    value = 0.0
  []
  [ss2_x]
    type = FunctionDirichletBC
    variable = u
    boundary = top
    function = ramp1
  []
[]

[Problem]
  type = FailingProblem
  fail_steps = '6'
[]

[Executioner]
  type = Transient
  solve_type = 'NEWTON'

  nl_max_its = 15
  nl_rel_tol = 1e-14
  nl_abs_tol = 1e-14
  l_tol = 1e-14

  start_time = 0.0
  end_time = 1.0

  [TimeStepper]
    type = ConstantDT
    dt = 0.1
    cutback_factor_at_failure = 0.5
  []

  [Predictor]
    type = SimplePredictor
    scale = 1.0
    skip_after_failed_timestep = true
  []
[]

[Postprocessors]
  [final_residual]
    type = Residual
    residual_type = FINAL
  []
  [initial_residual]
    type = Residual
    residual_type = INITIAL
  []
[]

[Outputs]
  csv = true
[]

(test/tests/predictors/simple/predictor_skip_old_test.i)

# The purpose of this test is to test the simple predictor.  This is a very
# small, monotonically loaded block of material.  If things are working right,
# the predictor should come very close to exactly nailing the solution on steps
# after the first step.

#This test checks to see that the predictor is skipped in the last step.

[Mesh]
  type = GeneratedMesh
  dim = 2
  xmin = 0
  xmax = 1
  ymin = 0
  ymax = 1
  nx = 3
  ny = 3
[]

[Functions]
  [ramp1]
    type = ParsedFunction
    expression = 't'
  []
[]

[Variables]
  [u]
    order = FIRST
    family = LAGRANGE
  []
[]

[Kernels]
  [diff_u]
    type = Diffusion
    variable = u
  []
[]

[BCs]
  [bot]
    type = DirichletBC
    variable = u
    boundary = bottom
    value = 0.0
  []
  [ss2_x]
    type = FunctionDirichletBC
    variable = u
    boundary = top
    function = ramp1
  []
[]

[Executioner]
  type = Transient
  solve_type = 'PJFNK'

  nl_max_its = 15
  nl_rel_tol = 1e-14
  nl_abs_tol = 1e-14

  start_time = 0.0
  dt = 0.5
  end_time = 1.5

  [Predictor]
    type = SimplePredictor
    scale = 1.0
    skip_times_old = '1.0'
  []
[]

[Postprocessors]
  [final_residual]
    type = Residual
    residual_type = FINAL
  []
  [initial_residual]
    type = Residual
    residual_type = INITIAL
  []
[]

[Outputs]
  csv = true
[]

Example input syntax
Input Parameters
Input Files