problem: !SequentialCoupling
  mesh:
    regions:
      - !From_ID
        name: A
        id: 1
      - name: B
        label: X
      - !From_Elements
        name: C
        id: 3
        element_list: [2, 3]
      - !Union
        name: F
        regions: [D, E]
      - !Union
        name: E
        regions: [F, G]
      - !Union
        name: D
        region_ids: [5, 6]
      - !Intersection
        name: G
        intersection: [F, E]
      - !Difference
        name: H
        difference: [G, E]
  secondary_equation_1: !Coupling_OperatorSplitting
    transport: !Solute_Advection_FV
      input_fields:
        - region: domain
          init_conc: 0
        - region: .left
          bc_type: dirichlet
          bc_conc: 10
          time: 0.0
    output_stream:
      file: ./transport.pvd
      format: !vtk
        variant: ascii
      time_step: 0.1
      name: transport_output_stream
    substances:
      - conc
    reaction_term: !Sorption
      solvent_density: 1.0
    time:
      end_time: 2.0
    balance:
      cumulative: true

  secondary_equation_2: !Coupling_OperatorSplitting
    transport: !SoluteTransport_DG
      input_fields:
        - r_set: BOUNDARY
          bc_conc: 0
        - rid: 20
          init_conc: 0
          diff_m: 0.1
        - rid: 24
          init_conc: 0
          diff_m: 0.1
          dg_penalty: 100
        - rid: 30
          init_conc: 1
      solver: !Petsc
        a_tol: 1.0e-12
        r_tol: 1.0e-12
    output_stream:
      file: ./transport-implicit.pvd
      format: !vtk
        variant: ascii
      time_step: 0.001
      name: transport_output_stream
    substances:
      - A
    time:
      end_time: 0.01
      max_dt: 0.001
    balance:
      cumulative: true
  # comment heat    
  secondary_equation_3: !Heat_AdvectionDiffusion_DG
    input_fields:
      - r_set: BOUNDARY
        bc_conc: 0
      - rid: 20
        init_conc: 0
        diff_m: 0.1
    solver: !Petsc
      a_tol: 1.0e-12
      r_tol: 1.0e-12
    substances:
      - A
