problem: !SequentialCoupling
  description: Zero flow + transport with source. Substance A - increase of concentration,
    B - decrease of concentration, C - rapid increase of concentration with high sigma,
    such that it determines CFL condition (t equals 1/(10/0.9)).
  mesh:
    mesh_file: ./input/test16_small.msh
  primary_equation: !Steady_MH
    n_schurs: 2
    input_fields:
      - r_set: ALL
        conductivity: 1.0e-10
      - region: .boundary
        bc_type: dirichlet
        bc_pressure: 0
    output:
      output_stream: 
        file: ./flow_test16.pvd
        format: !vtk
          variant: ascii
        name: flow_output_stream
      output_fields:
        - pressure_p0
        - pressure_p1
        - velocity_p0
    balance:
      cumulative: true
    solver: !Petsc
      a_tol: 1.0e-12
      r_tol: 1.0e-12
  secondary_equation: !TransportOperatorSplitting
    input_fields:
      - region: .boundary
        bc_conc: 0
      - r_set: ALL
        init_conc:
          - 0
          - 0.9
          - 0
        sources_sigma:
          - 3
          - 3
          - 10
        sources_conc:
          - 0.6
          - 0.6
          - 0.6
        porosity: 0.9
    output_stream: 
      file: ./transport_test16.pvd
      format: !vtk
        variant: ascii
      time_step: 0.2
    substances:
      - A
      - B
      - C
    balance:
      cumulative: true
    time:
      end_time: 1.0