text: #################################################################################
  # The Institute for the Design of Advanced Energy Systems Integrated Platform
  # Framework (IDAES IP) was produced under the DOE Institute for the
  # Design of Advanced Energy Systems (IDAES), and is copyright (c) 2018-2021
  # by the software owners: The Regents of the University of California, through
  # Lawrence Berkeley National Laboratory,  National Technology & Engineering
  # Solutions of Sandia, LLC, Carnegie Mellon University, West Virginia University
  # Research Corporation, et al.  All rights reserved.
  #
  # Please see the files COPYRIGHT.md and LICENSE.md for full copyright and
  # license information.
  #################################################################################
  """
  General purpose mixer block for IDAES models
  """
  from enum import Enum
  
  from pyomo.environ import (
      Constraint,
      Param,
      PositiveReals,
      Reals,
      RangeSet,
      Var,
  )
  from pyomo.common.config import ConfigBlock, ConfigValue, In, ListOf, Bool
  
  from idaes.core import (
      declare_process_block_class,
      UnitModelBlockData,
      useDefault,
      MaterialBalanceType,
      MaterialFlowBasis
  )
  from idaes.core.util.config import (
      is_physical_parameter_block,
      is_state_block,
  )
  from idaes.core.util.exceptions import (
      BurntToast,
      ConfigurationError,
      PropertyNotSupportedError,
  )
  from idaes.core.util.math import smooth_min
  from idaes.core.util.tables import create_stream_table_dataframe
  import idaes.core.util.scaling as iscale
  from idaes.core.util import get_solver
  
  import idaes.logger as idaeslog
  
  __author__ = "Andrew Lee"
  
  
  # Set up logger
  _log = idaeslog.getLogger(__name__)
  
  
  # Enumerate options for balances
  class MixingType(Enum):
      none = 0
      extensive = 1
  
  
  class MomentumMixingType(Enum):
      none = 0
      minimize = 1
      equality = 2
      minimize_and_equality = 3
  
  
  @declare_process_block_class("Mixer")
  class MixerData(UnitModelBlockData):
      """
      This is a general purpose model for a Mixer block with the IDAES modeling
      framework. This block can be used either as a stand-alone Mixer unit
      operation, or as a sub-model within another unit operation.
  
      This model creates a number of StateBlocks to represent the incoming
      streams, then writes a set of phase-component material balances, an
      overall enthalpy balance and a momentum balance (2 options) linked to a
      mixed-state StateBlock. The mixed-state StateBlock can either be specified
      by the user (allowing use as a sub-model), or created by the Mixer.
  
      When being used as a sub-model, Mixer should only be used when a set
      of new StateBlocks are required for the streams to be mixed. It should not
      be used to mix streams from mutiple ControlVolumes in a single unit model -
      in these cases the unit model developer should write their own mixing
      equations.
      """
  
      CONFIG = ConfigBlock()
      CONFIG.declare(
          "dynamic",
          ConfigValue(
              domain=In([False]),
              default=False,
              description="Dynamic model flag - must be False",
              doc="""Indicates whether this model will be dynamic or not,
  **default** = False. Mixer blocks are always steady-state.""",
          ),
      )
      CONFIG.declare(
          "has_holdup",
          ConfigValue(
              default=False,
              domain=In([False]),
              description="Holdup construction flag - must be False",
              doc="""Mixer blocks do not contain holdup, thus this must be
  False.""",
          ),
      )
      CONFIG.declare(
          "property_package",
          ConfigValue(
              default=useDefault,
              domain=is_physical_parameter_block,
              description="Property package to use for mixer",
              doc="""Property parameter object used to define property
  calculations, **default** - useDefault.
  **Valid values:** {
  **useDefault** - use default package from parent model or flowsheet,
  **PropertyParameterObject** - a PropertyParameterBlock object.}""",
          ),
      )
      CONFIG.declare(
          "property_package_args",
          ConfigBlock(
              implicit=True,
              description="Arguments to use for constructing property packages",
              doc="""A ConfigBlock with arguments to be passed to a property
  block(s) and used when constructing these,
  **default** - None.
  **Valid values:** {
  see property package for documentation.}""",
          ),
      )
      CONFIG.declare(
          "inlet_list",
          ConfigValue(
              domain=ListOf(str),
              description="List of inlet names",
              doc="""A list containing names of inlets,
  **default** - None.
  **Valid values:** {
  **None** - use num_inlets argument,
  **list** - a list of names to use for inlets.}""",
          ),
      )
      CONFIG.declare(
          "num_inlets",
          ConfigValue(
              domain=int,
              description="Number of inlets to unit",
              doc="""Argument indicating number (int) of inlets to construct, not
  used if inlet_list arg is provided,
  **default** - None.
  **Valid values:** {
  **None** - use inlet_list arg instead, or default to 2 if neither argument
  provided,
  **int** - number of inlets to create (will be named with sequential integers
  from 1 to num_inlets).}""",
          ),
      )
      CONFIG.declare(
          "material_balance_type",
          ConfigValue(
              default=MaterialBalanceType.useDefault,
              domain=In(MaterialBalanceType),
              description="Material balance construction flag",
              doc="""Indicates what type of mass balance should be constructed,
  **default** - MaterialBalanceType.useDefault.
  **Valid values:** {
  **MaterialBalanceType.useDefault - refer to property package for default
  balance type
  **MaterialBalanceType.none** - exclude material balances,
  **MaterialBalanceType.componentPhase** - use phase component balances,
  **MaterialBalanceType.componentTotal** - use total component balances,
  **MaterialBalanceType.elementTotal** - use total element balances,
  **MaterialBalanceType.total** - use total material balance.}""",
          ),
      )
      CONFIG.declare(
          "has_phase_equilibrium",
          ConfigValue(
              default=False,
              domain=Bool,
              description="Calculate phase equilibrium in mixed stream",
              doc="""Argument indicating whether phase equilibrium should be
  calculated for the resulting mixed stream,
  **default** - False.
  **Valid values:** {
  **True** - calculate phase equilibrium in mixed stream,
  **False** - do not calculate equilibrium in mixed stream.}""",
          ),
      )
      CONFIG.declare(
          "energy_mixing_type",
          ConfigValue(
              default=MixingType.extensive,
              domain=MixingType,
              description="Method to use when mixing energy flows",
              doc="""Argument indicating what method to use when mixing energy
  flows of incoming streams,
  **default** - MixingType.extensive.
  **Valid values:** {
  **MixingType.none** - do not include energy mixing equations,
  **MixingType.extensive** - mix total enthalpy flows of each phase.}""",
          ),
      )
      CONFIG.declare(
          "momentum_mixing_type",
          ConfigValue(
              default=MomentumMixingType.minimize,
              domain=MomentumMixingType,
              description="Method to use when mixing momentum/pressure",
              doc="""Argument indicating what method to use when mixing momentum/
  pressure of incoming streams,
  **default** - MomentumMixingType.minimize.
  **Valid values:** {
  **MomentumMixingType.none** - do not include momentum mixing equations,
  **MomentumMixingType.minimize** - mixed stream has pressure equal to the
  minimimum pressure of the incoming streams (uses smoothMin operator),
  **MomentumMixingType.equality** - enforces equality of pressure in mixed and
  all incoming streams.,
  **MomentumMixingType.minimize_and_equality** - add constraints for pressure
  equal to the minimum pressure of the inlets and constraints for equality of
  pressure in mixed and all incoming streams. When the model is initially built,
  the equality constraints are deactivated.  This option is useful for switching
  between flow and pressure driven simulations.}""",
          ),
      )
      CONFIG.declare(
          "mixed_state_block",
          ConfigValue(
              default=None,
              domain=is_state_block,
              description="Existing StateBlock to use as mixed stream",
              doc="""An existing state block to use as the outlet stream from the
  Mixer block,
  **default** - None.
  **Valid values:** {
  **None** - create a new StateBlock for the mixed stream,
  **StateBlock** - a StateBock to use as the destination for the mixed stream.}
  """,
          ),
      )
      CONFIG.declare(
          "construct_ports",
          ConfigValue(
              default=True,
              domain=Bool,
              description="Construct inlet and outlet Port objects",
              doc="""Argument indicating whether model should construct Port
  objects linked to all inlet states and the mixed state,
  **default** - True.
  **Valid values:** {
  **True** - construct Ports for all states,
  **False** - do not construct Ports.""",
          ),
      )
  
      def build(self):
          """
          General build method for MixerData. This method calls a number
          of sub-methods which automate the construction of expected attributes
          of unit models.
  
          Inheriting models should call `super().build`.
  
          Args:
              None
  
          Returns:
              None
          """
          # Call super.build()
          super(MixerData, self).build()
  
          # Call setup methods from ControlVolumeBlockData
          self._get_property_package()
          self._get_indexing_sets()
  
          # Create list of inlet names
          inlet_list = self.create_inlet_list()
  
          # Build StateBlocks
          inlet_blocks = self.add_inlet_state_blocks(inlet_list)
  
          if self.config.mixed_state_block is None:
              mixed_block = self.add_mixed_state_block()
          else:
              mixed_block = self.get_mixed_state_block()
  
          mb_type = self.config.material_balance_type
          if mb_type == MaterialBalanceType.useDefault:
              t_ref = self.flowsheet().time.first()
              mb_type = mixed_block[t_ref].default_material_balance_type()
  
          if mb_type != MaterialBalanceType.none:
              self.add_material_mixing_equations(
                  inlet_blocks=inlet_blocks,
                  mixed_block=mixed_block,
                  mb_type=mb_type
              )
          else:
              raise BurntToast(
                  "{} received unrecognised value for "
                  "material_mixing_type argument. This "
                  "should not occur, so please contact "
                  "the IDAES developers with this bug.".format(self.name)
              )
  
          if self.config.energy_mixing_type == MixingType.extensive:
              self.add_energy_mixing_equations(
                  inlet_blocks=inlet_blocks, mixed_block=mixed_block
              )
          elif self.config.energy_mixing_type == MixingType.none:
              pass
          else:
              raise ConfigurationError(
                  "{} received unrecognised value for "
                  "material_mixing_type argument. This "
                  "should not occur, so please contact "
                  "the IDAES developers with this bug.".format(self.name)
              )
  
          # Add to try/expect to catch cases where pressure is not supported
          # by properties.
          try:
              if self.config.momentum_mixing_type == MomentumMixingType.minimize:
                  self.add_pressure_minimization_equations(
                      inlet_blocks=inlet_blocks, mixed_block=mixed_block
                  )
              elif (self.config.momentum_mixing_type ==
                      MomentumMixingType.equality):
                  self.add_pressure_equality_equations(
                      inlet_blocks=inlet_blocks, mixed_block=mixed_block
                  )
              elif (
                  self.config.momentum_mixing_type ==
                  MomentumMixingType.minimize_and_equality
              ):
                  self.add_pressure_minimization_equations(
                      inlet_blocks=inlet_blocks, mixed_block=mixed_block
                  )
                  self.add_pressure_equality_equations(
                      inlet_blocks=inlet_blocks, mixed_block=mixed_block
                  )
                  self.pressure_equality_constraints.deactivate()
              elif self.config.momentum_mixing_type == MomentumMixingType.none:
                  pass
              else:
                  raise ConfigurationError(
                      "{} recieved unrecognised value for "
                      "momentum_mixing_type argument. This "
                      "should not occur, so please contact "
                      "the IDAES developers with this bug.".format(self.name)
                      )
          except PropertyNotSupportedError:
              raise PropertyNotSupportedError(
                  "{} The property package supplied for this unit does not "
                  "appear to support pressure, which is required for momentum "
                  "mixing. Please set momentum_mixing_type to "
                  "MomentumMixingType.none or provide a property package which "
                  "supports pressure.".format(self.name))
  
          self.add_port_objects(inlet_list, inlet_blocks, mixed_block)
  
      def create_inlet_list(self):
          """
          Create list of inlet stream names based on config arguments.
  
          Returns:
              list of strings
          """
          if (self.config.inlet_list is not None and
                  self.config.num_inlets is not None):
              # If both arguments provided and not consistent, raise Exception
              if len(self.config.inlet_list) != self.config.num_inlets:
                  raise ConfigurationError(
                      "{} Mixer provided with both inlet_list and "
                      "num_inlets arguments, which were not consistent ("
                      "length of inlet_list was not equal to num_inlets). "
                      "PLease check your arguments for consistency, and "
                      "note that it is only necessary to provide one of "
                      "these arguments.".format(self.name)
                  )
          elif self.config.inlet_list is None and self.config.num_inlets is None:
              # If no arguments provided for inlets, default to num_inlets = 2
              self.config.num_inlets = 2
  
          # Create a list of names for inlet StateBlocks
          if self.config.inlet_list is not None:
              inlet_list = self.config.inlet_list
          else:
              inlet_list = [
                  "inlet_" + str(n) for n in range(1, self.config.num_inlets + 1)
              ]
  
          return inlet_list
  
      def add_inlet_state_blocks(self, inlet_list):
          """
          Construct StateBlocks for all inlet streams.
  
          Args:
              list of strings to use as StateBlock names
  
          Returns:
              list of StateBlocks
          """
          # Setup StateBlock argument dict
          tmp_dict = dict(**self.config.property_package_args)
          tmp_dict["has_phase_equilibrium"] = False
          tmp_dict["defined_state"] = True
  
          # Create empty list to hold StateBlocks for return
          inlet_blocks = []
  
          # Create an instance of StateBlock for all inlets
          for i in inlet_list:
              i_obj = self.config.property_package.build_state_block(
                  self.flowsheet().time,
                  doc="Material properties at inlet",
                  default=tmp_dict,
              )
  
              setattr(self, i + "_state", i_obj)
  
              inlet_blocks.append(getattr(self, i + "_state"))
  
          return inlet_blocks
  
      def add_mixed_state_block(self):
          """
          Constructs StateBlock to represent mixed stream.
  
          Returns:
              New StateBlock object
          """
          # Setup StateBlock argument dict
          tmp_dict = dict(**self.config.property_package_args)
          tmp_dict["has_phase_equilibrium"] = self.config.has_phase_equilibrium
          tmp_dict["defined_state"] = False
  
          self.mixed_state = self.config.property_package.build_state_block(
              self.flowsheet().time,
              doc="Material properties of mixed stream",
              default=tmp_dict,
          )
  
          return self.mixed_state
  
      def get_mixed_state_block(self):
          """
          Validates StateBlock provided in user arguments for mixed stream.
  
          Returns:
              The user-provided StateBlock or an Exception
          """
          # Sanity check to make sure method is not called when arg missing
          if self.config.mixed_state_block is None:
              raise BurntToast(
                  "{} get_mixed_state_block method called when "
                  "mixed_state_block argument is None. This should "
                  "not happen.".format(self.name)
              )
  
          # Check that the user-provided StateBlock uses the same prop pack
          if (
              self.config.mixed_state_block[
                  self.flowsheet().time.first()
              ].config.parameters
              != self.config.property_package
          ):
              raise ConfigurationError(
                  "{} StateBlock provided in mixed_state_block argument "
                  "does not come from the same property package as "
                  "provided in the property_package argument. All "
                  "StateBlocks within a Mixer must use the same "
                  "property package.".format(self.name)
              )
  
          return self.config.mixed_state_block
  
      def add_material_mixing_equations(self, inlet_blocks,
                                        mixed_block, mb_type):
          """
          Add material mixing equations.
          """
          pp = self.config.property_package
          # Get phase component list(s)
          pc_set = mixed_block.phase_component_set
  
          # Get units metadata
          units = pp.get_metadata()
  
          flow_basis = mixed_block[
              self.flowsheet().time.first()].get_material_flow_basis()
          if flow_basis == MaterialFlowBasis.molar:
              flow_units = units.get_derived_units("flow_mole")
          elif flow_basis == MaterialFlowBasis.mass:
              flow_units = units.get_derived_units("flow_mass")
          else:
              # Let this pass for now with no units
              flow_units = None
  
          if mb_type == MaterialBalanceType.componentPhase:
              # Create equilibrium generation term and constraints if required
              if self.config.has_phase_equilibrium is True:
                  try:
                      self.phase_equilibrium_generation = Var(
                          self.flowsheet().time,
                          pp.phase_equilibrium_idx,
                          domain=Reals,
                          doc="Amount of generation in unit by phase equilibria",
                          units=flow_units
                      )
                  except AttributeError:
                      raise PropertyNotSupportedError(
                          "{} Property package does not contain a list of phase "
                          "equilibrium reactions (phase_equilibrium_idx), "
                          "thus does not support phase equilibrium."
                          .format(self.name)
                      )
  
              # Define terms to use in mixing equation
              def phase_equilibrium_term(b, t, p, j):
                  if self.config.has_phase_equilibrium:
                      sd = {}
                      for r in pp.phase_equilibrium_idx:
                          if pp.phase_equilibrium_list[r][0] == j:
                              if (
                                  pp.phase_equilibrium_list[r][1][
                                      0
                                  ]
                                  == p
                              ):
                                  sd[r] = 1
                              elif (
                                  pp.phase_equilibrium_list[r][1][
                                      1
                                  ]
                                  == p
                              ):
                                  sd[r] = -1
                              else:
                                  sd[r] = 0
                          else:
                              sd[r] = 0
  
                      return sum(
                          b.phase_equilibrium_generation[t, r] * sd[r] for r in
                          pp.phase_equilibrium_idx
                      )
                  else:
                      return 0
  
              # Write phase-component balances
              @self.Constraint(
                  self.flowsheet().time,
                  pc_set,
                  doc="Material mixing equations",
              )
              def material_mixing_equations(b, t, p, j):
                  return 0 == (
                      sum(
                          inlet_blocks[i][t].get_material_flow_terms(p, j)
                          for i in range(len(inlet_blocks))
                      )
                      - mixed_block[t].get_material_flow_terms(p, j)
                      + phase_equilibrium_term(b, t, p, j)
                  )
  
          elif mb_type == MaterialBalanceType.componentTotal:
              # Write phase-component balances
              @self.Constraint(
                  self.flowsheet().time,
                  mixed_block.component_list,
                  doc="Material mixing equations",
              )
              def material_mixing_equations(b, t, j):
                  return 0 == sum(
                      sum(
                          inlet_blocks[i][t].get_material_flow_terms(p, j)
                          for i in range(len(inlet_blocks))
                      )
                      - mixed_block[t].get_material_flow_terms(p, j)
                      for p in mixed_block.phase_list
                      if (p, j) in pc_set
                  )
  
          elif mb_type == MaterialBalanceType.total:
              # Write phase-component balances
              @self.Constraint(
                  self.flowsheet().time, doc="Material mixing equations"
              )
              def material_mixing_equations(b, t):
                  return 0 == sum(
                      sum(
                          sum(
                              inlet_blocks[i][t].get_material_flow_terms(p, j)
                              for i in range(len(inlet_blocks))
                          )
                          - mixed_block[t].get_material_flow_terms(p, j)
                          for j in mixed_block.component_list
                          if (p, j) in pc_set
                      )
                      for p in mixed_block.phase_list
                  )
  
          elif mb_type == MaterialBalanceType.elementTotal:
              raise ConfigurationError(
                  "{} Mixers do not support elemental "
                  "material balances.".format(self.name)
              )
          elif mb_type == MaterialBalanceType.none:
              pass
          else:
              raise BurntToast(
                  "{} Mixer received unrecognised value for "
                  "material_balance_type. This should not happen, "
                  "please report this bug to the IDAES developers."
                  .format(self.name)
              )
  
      def add_energy_mixing_equations(self, inlet_blocks, mixed_block):
          """
          Add energy mixing equations (total enthalpy balance).
          """
  
          @self.Constraint(self.flowsheet().time, doc="Energy balances")
          def enthalpy_mixing_equations(b, t):
              return 0 == (
                  sum(
                      sum(
                          inlet_blocks[i][t].get_enthalpy_flow_terms(p)
                          for p in mixed_block.phase_list
                      )
                      for i in range(len(inlet_blocks))
                  )
                  - sum(
                      mixed_block[t].get_enthalpy_flow_terms(p)
                      for p in mixed_block.phase_list
                  )
              )
  
      def add_pressure_minimization_equations(self, inlet_blocks, mixed_block):
          """
          Add pressure minimization equations. This is done by sequential
          comparisons of each inlet to the minimum pressure so far, using
          the IDAES smooth minimum fuction.
          """
          if not hasattr(self, "inlet_idx"):
              self.inlet_idx = RangeSet(len(inlet_blocks))
  
          # Get units metadata
          units = self.config.property_package.get_metadata()
  
          # Add variables
          self.minimum_pressure = Var(
              self.flowsheet().time,
              self.inlet_idx,
              doc="Variable for calculating minimum inlet pressure",
              units=units.get_derived_units("pressure")
          )
  
          self.eps_pressure = Param(
              mutable=True,
              initialize=1e-3,
              domain=PositiveReals,
              doc="Smoothing term for minimum inlet pressure",
              units=units.get_derived_units("pressure")
          )
  
          # Calculate minimum inlet pressure
          @self.Constraint(
              self.flowsheet().time,
              self.inlet_idx,
              doc="Calculation for minimum inlet pressure",
          )
          def minimum_pressure_constraint(b, t, i):
              if i == self.inlet_idx.first():
                  return self.minimum_pressure[t, i] == (
                      inlet_blocks[i - 1][t].pressure)
              else:
                  return self.minimum_pressure[t, i] == (
                      smooth_min(
                          self.minimum_pressure[t, i - 1],
                          inlet_blocks[i - 1][t].pressure,
                          self.eps_pressure,
                      )
                  )
  
          # Set inlet pressure to minimum pressure
          @self.Constraint(
              self.flowsheet().time, doc="Link pressure to control volume"
          )
          def mixture_pressure(b, t):
              return mixed_block[t].pressure == (
                  self.minimum_pressure[t, self.inlet_idx.last()]
              )
  
      def add_pressure_equality_equations(self, inlet_blocks, mixed_block):
          """
          Add pressure equality equations. Note that this writes a number of
          constraints equal to the number of inlets, enforcing equality between
          all inlets and the mixed stream.
          """
          if not hasattr(self, "inlet_idx"):
              self.inlet_idx = RangeSet(len(inlet_blocks))
  
          # Create equality constraints
          @self.Constraint(
              self.flowsheet().time,
              self.inlet_idx,
              doc="Calculation for minimum inlet pressure",
          )
          def pressure_equality_constraints(b, t, i):
              return mixed_block[t].pressure == inlet_blocks[i - 1][t].pressure
  
      def add_port_objects(self, inlet_list, inlet_blocks, mixed_block):
          """
          Adds Port objects if required.
  
          Args:
              a list of inlet StateBlock objects
              a mixed state StateBlock object
  
          Returns:
              None
          """
          if self.config.construct_ports is True:
              # Add ports
              for p in inlet_list:
                  i_state = getattr(self, p + "_state")
                  self.add_port(name=p, block=i_state, doc="Inlet Port")
              self.add_port(name="outlet", block=mixed_block, doc="Outlet Port")
  
      def model_check(blk):
          """
          This method executes the model_check methods on the associated state
          blocks (if they exist). This method is generally called by a unit model
          as part of the unit's model_check method.
  
          Args:
              None
  
          Returns:
              None
          """
          # Try property block model check
          for t in blk.flowsheet().time:
              try:
                  inlet_list = blk.create_inlet_list()
                  for i in inlet_list:
                      i_block = getattr(blk, i + "_state")
                      i_block[t].model_check()
              except AttributeError:
                  _log.warning(
                      "{} Mixer inlet property block has no model "
                      "checks. To correct this, add a model_check "
                      "method to the associated StateBlock class."
                      .format(blk.name)
                  )
              try:
                  if blk.config.mixed_state_block is None:
                      blk.mixed_state[t].model_check()
                  else:
                      blk.config.mixed_state_block.model_check()
              except AttributeError:
                  _log.warning(
                      "{} Mixer outlet property block has no "
                      "model checks. To correct this, add a "
                      "model_check method to the associated "
                      "StateBlock class.".format(blk.name)
                  )
  
      def use_minimum_inlet_pressure_constraint(self):
          """Activate the mixer pressure = mimimum inlet pressure constraint and
          deactivate the mixer pressure and all inlet pressures are equal
          constraints. This should only be used when momentum_mixing_type ==
          MomentumMixingType.minimize_and_equality.
          """
          if (self.config.momentum_mixing_type !=
                  MomentumMixingType.minimize_and_equality):
              _log.warning(
                  """use_minimum_inlet_pressure_constraint() can only be used
                  when momentum_mixing_type ==
                  MomentumMixingType.minimize_and_equality"""
              )
              return
          self.minimum_pressure_constraint.activate()
          self.pressure_equality_constraints.deactivate()
  
      def use_equal_pressure_constraint(self):
          """Deactivate the mixer pressure = mimimum inlet pressure constraint
          and activate the mixer pressure and all inlet pressures are equal
          constraints. This should only be used when momentum_mixing_type ==
          MomentumMixingType.minimize_and_equality.
          """
          if (self.config.momentum_mixing_type !=
                  MomentumMixingType.minimize_and_equality):
              _log.warning(
                  """use_equal_pressure_constraint() can only be used when
                  momentum_mixing_type ==
                  MomentumMixingType.minimize_and_equality"""
              )
              return
          self.minimum_pressure_constraint.deactivate()
          self.pressure_equality_constraints.activate()
  
      def initialize(blk, outlvl=idaeslog.NOTSET, optarg=None,
                     solver=None, hold_state=False):
          """
          Initialization routine for mixer.
  
          Keyword Arguments:
              outlvl : sets output level of initialization routine
              optarg : solver options dictionary object (default=None, use
                       default solver options)
              solver : str indicating which solver to use during
                       initialization (default = None, use default solver)
              hold_state : flag indicating whether the initialization routine
                       should unfix any state variables fixed during
                       initialization, **default** - False. **Valid values:**
                       **True** - states variables are not unfixed, and a dict of
                       returned containing flags for which states were fixed
                       during initialization, **False** - state variables are
                       unfixed after initialization by calling the release_state
                       method.
  
          Returns:
              If hold_states is True, returns a dict containing flags for which
              states were fixed during initialization.
          """
          init_log = idaeslog.getInitLogger(blk.name, outlvl, tag="unit")
          solve_log = idaeslog.getSolveLogger(blk.name, outlvl, tag="unit")
  
          # Create solver
          opt = get_solver(solver, optarg)
  
          # Initialize inlet state blocks
          flags = {}
          inlet_list = blk.create_inlet_list()
          i_block_list = []
          for i in inlet_list:
              i_block = getattr(blk, i + "_state")
              i_block_list.append(i_block)
              flags[i] = {}
              flags[i] = i_block.initialize(
                  outlvl=outlvl,
                  optarg=optarg,
                  solver=solver,
                  hold_state=True,
              )
  
          # Initialize mixed state block
          if blk.config.mixed_state_block is None:
              mblock = blk.mixed_state
          else:
              mblock = blk.config.mixed_state_block
  
          o_flags = {}
          # Calculate initial guesses for mixed stream state
          for t in blk.flowsheet().time:
              # Iterate over state vars as defined by property package
              s_vars = mblock[t].define_state_vars()
              for s in s_vars:
                  i_vars = []
                  for k in s_vars[s]:
                      # Record whether variable was fixed or not
                      o_flags[t, s, k] = s_vars[s][k].fixed
  
                      # If fixed, use current value
                      # otherwise calculate guess from mixed state
                      if not s_vars[s][k].fixed:
                          for i in range(len(i_block_list)):
                              i_vars.append(
                                  getattr(i_block_list[i][t],
                                          s_vars[s].local_name)
                              )
  
                          if s == "pressure":
                              # If pressure, use minimum as initial guess
                              mblock[t].pressure.value = min(
                                  i_block_list[i][t].pressure.value
                                  for i in range(len(i_block_list))
                              )
                          elif "flow" in s:
                              # If a "flow" variable (i.e. extensive), sum inlets
                              for k in s_vars[s]:
                                  s_vars[s][k].value = sum(
                                      i_vars[i][k].value for i in range(
                                          len(i_block_list))
                                  )
                          else:
                              # Otherwise use average of inlets
                              for k in s_vars[s]:
                                  s_vars[s][k].value = sum(
                                      i_vars[i][k].value for i in range(
                                          len(i_block_list))
                                  ) / len(i_block_list)
  
          mblock.initialize(
              outlvl=outlvl,
              optarg=optarg,
              solver=solver,
              hold_state=False,
          )
  
          # Revert fixed status of variables to what they were before
          for t in blk.flowsheet().time:
              s_vars = mblock[t].define_state_vars()
              for s in s_vars:
                  for k in s_vars[s]:
                      s_vars[s][k].fixed = o_flags[t, s, k]
  
          if blk.config.mixed_state_block is None:
              if (
                  hasattr(blk, "pressure_equality_constraints")
                  and blk.pressure_equality_constraints.active is True
              ):
                  blk.pressure_equality_constraints.deactivate()
                  for t in blk.flowsheet().time:
                      sys_press = getattr(
                          blk,
                          blk.create_inlet_list()[0] + "_state")[t].pressure
                      blk.mixed_state[t].pressure.fix(sys_press.value)
                  with idaeslog.solver_log(solve_log, idaeslog.DEBUG)as slc:
                      res = opt.solve(blk, tee=slc.tee)
                  blk.pressure_equality_constraints.activate()
                  for t in blk.flowsheet().time:
                      blk.mixed_state[t].pressure.unfix()
              else:
                  with idaeslog.solver_log(solve_log, idaeslog.DEBUG) as slc:
                      res = opt.solve(blk, tee=slc.tee)
  
              init_log.info(
                  "Initialization Complete: {}".format(idaeslog.condition(res))
              )
          else:
              init_log.info("Initialization Complete.")
  
          if hold_state is True:
              return flags
          else:
              blk.release_state(flags, outlvl=outlvl)
  
      def release_state(blk, flags, outlvl=idaeslog.NOTSET):
          """
          Method to release state variables fixed during initialization.
  
          Keyword Arguments:
              flags : dict containing information of which state variables
                      were fixed during initialization, and should now be
                      unfixed. This dict is returned by initialize if
                      hold_state = True.
              outlvl : sets output level of logging
  
          Returns:
              None
          """
          inlet_list = blk.create_inlet_list()
          for i in inlet_list:
              i_block = getattr(blk, i + "_state")
              i_block.release_state(flags[i], outlvl=outlvl)
  
      def _get_stream_table_contents(self, time_point=0):
          io_dict = {}
          inlet_list = self.create_inlet_list()
          for i in inlet_list:
              io_dict[i] = getattr(self, i + "_state")
          if self.config.mixed_state_block is None:
              io_dict["Outlet"] = self.mixed_state
          else:
              io_dict["Outlet"] = self.config.mixed_state_block
          return create_stream_table_dataframe(io_dict, time_point=time_point)
  
      def calculate_scaling_factors(self):
          super().calculate_scaling_factors()
          mb_type = self.config.material_balance_type
          if mb_type == MaterialBalanceType.useDefault:
              t_ref = self.flowsheet().time.first()
              mb_type = self.mixed_state[t_ref].default_material_balance_type()
  
          if hasattr(self, "pressure_equality_constraints"):
              for (t, i), c in self.pressure_equality_constraints.items():
                  s = iscale.get_scaling_factor(
                      self.mixed_state[t].pressure, default=1, warning=True)
                  iscale.constraint_scaling_transform(c, s)
  
          if hasattr(self, "material_mixing_equations"):
              if mb_type == MaterialBalanceType.componentPhase:
                  for (t, p, j), c in self.material_mixing_equations.items():
                      flow_term = self.mixed_state[t].get_material_flow_terms(p, j)
                      s = iscale.get_scaling_factor(flow_term, default=1)
                      iscale.constraint_scaling_transform(c, s, overwrite=False)
              elif mb_type == MaterialBalanceType.componentTotal:
                  for (t, j), c in self.material_mixing_equations.items():
                      for i, p in enumerate(self.mixed_state.phase_list):
                          try:
                              ft = self.mixed_state[t].get_material_flow_terms(p, j)
                          except (KeyError, AttributeError):
                              continue # component not in phase
                          if i == 0:
                              s = iscale.get_scaling_factor(ft, default=1)
                          else:
                              _s = iscale.get_scaling_factor(ft, default=1)
                              s = _s if _s < s else s
                      iscale.constraint_scaling_transform(c, s, overwrite=False)
              elif mb_type == MaterialBalanceType.total:
                  pc_set = self.mixed_state.phase_component_set
                  for t, c in self.material_mixing_equations.items():
                      for i, (p, j) in enumerate(pc_set):
                          ft = self.mixed_state[t].get_material_flow_terms(p, j)
                          if i == 0:
                              s = iscale.get_scaling_factor(ft, default=1)
                          else:
                              _s = iscale.get_scaling_factor(ft, default=1)
                              s = _s if _s < s else s
                      iscale.constraint_scaling_transform(c, s, overwrite=False)
  
          if hasattr(self, "enthalpy_mixing_equations"):
              for t, c in self.enthalpy_mixing_equations.items():
                  def scale_gen():
                      for v in self.mixed_state[t].phase_list:
                          yield self.mixed_state[t].get_enthalpy_flow_terms(p)
  
                  s = iscale.min_scaling_factor(
                      scale_gen(),
                      default=1)
                  iscale.constraint_scaling_transform(c, s, overwrite=False)
  