setgradientboundarycondition_DGModel1D_t Subroutine

  subroutine setgradientboundarycondition_DGModel1D_t(this)
    ! Here, we set the boundary conditions for the
    ! solution and the solution gradient at the left
    ! and right most boundaries.
    !
    ! Here, we use periodic boundary conditions
    implicit none
    class(DGModel1D_t),intent(inout) :: this
    ! local
    real(prec) :: x
    integer :: nelem

    nelem = this%geometry%nelem ! number of elements in the mesh

    ! left-most boundary
    if(this%mesh%bcid(1) == SELF_BC_PRESCRIBED) then

      x = this%geometry%x%boundary(1,1,1)
      this%solutionGradient%extBoundary(1,1,1:this%nvar) = &
        this%pbc1d_Prescribed(x,this%t)

    elseif(this%mesh%bcid(1) == SELF_BC_RADIATION) then

      this%solutionGradient%extBoundary(1,1,1:this%nvar) = &
        this%pbc1d_Radiation(this%solutionGradient%boundary(1,1,1:this%nvar),-1.0_prec)

    elseif(this%mesh%bcid(1) == SELF_BC_NONORMALFLOW) then

      this%solutionGradient%extBoundary(1,1,1:this%nvar) = &
        this%pbc1d_NoNormalFlow(this%solutionGradient%boundary(1,1,1:this%nvar),-1.0_prec)

    else ! Periodic

      this%solutionGradient%extBoundary(1,1,1:this%nvar) = this%solutionGradient%boundary(2,nelem,1:this%nvar)

    endif

    ! right-most boundary
    if(this%mesh%bcid(1) == SELF_BC_PRESCRIBED) then

      x = this%geometry%x%boundary(2,nelem,1)
      this%solutionGradient%extBoundary(2,nelem,1:this%nvar) = &
        this%pbc1d_Prescribed(x,this%t)

    elseif(this%mesh%bcid(1) == SELF_BC_RADIATION) then

      this%solutionGradient%extBoundary(2,nelem,1:this%nvar) = &
        this%pbc1d_Radiation(this%solutionGradient%boundary(2,nelem,1:this%nvar),-1.0_prec)

    elseif(this%mesh%bcid(1) == SELF_BC_NONORMALFLOW) then

      this%solutionGradient%extBoundary(2,nelem,1:this%nvar) = &
        this%pbc1d_NoNormalFlow(this%solutionGradient%boundary(2,nelem,1:this%nvar),-1.0_prec)

    else ! Periodic

      this%solutionGradient%extBoundary(2,nelem,1:this%nvar) = this%solutionGradient%boundary(1,1,1:this%nvar)

    endif

  endsubroutine setgradientboundarycondition_DGModel1D_t