hbc2d_Radiation_LinearEuler2D Subroutine

  subroutine hbc2d_Radiation_LinearEuler2D(bc,mymodel)
    !! Radiation BC: zero acoustic perturbation in the exterior state; the
    !! sound speed (variable 5) and background density (variable 6) are copied
    !! from the interior side so the Riemann solver sees a consistent c and
    !! rho0 (impedance-matched, non-reflecting outflow).
    class(BoundaryCondition),intent(in) :: bc
    class(Model),intent(inout) :: mymodel
    ! Local
    integer :: n,i,iEl,j

    select type(m => mymodel)
    class is(LinearEuler2D_t)
      do n = 1,bc%nBoundaries
        iEl = bc%elements(n)
        j = bc%sides(n)
        do i = 1,m%solution%interp%N+1
          m%solution%extBoundary(i,j,iEl,1:4) = 0.0_prec
          m%solution%extBoundary(i,j,iEl,5) = m%solution%boundary(i,j,iEl,5) ! c preserved
          m%solution%extBoundary(i,j,iEl,6) = m%solution%boundary(i,j,iEl,6) ! rho0 preserved
        enddo
      enddo
    endselect

  endsubroutine hbc2d_Radiation_LinearEuler2D