BoundaryFlux_DGModel3D Subroutine

  subroutine BoundaryFlux_DGModel3D(this)
    ! this method uses an linear upwind solver for the
    ! advective flux and the bassi-rebay method for the
    ! diffusive fluxes
    implicit none
    class(DGModel3D),intent(inout) :: this
    ! Local
    integer :: i,j,k,iel
    real(prec) :: sL(1:this%nvar),sR(1:this%nvar)
    real(prec) :: dsdx(1:this%nvar,1:3)
    real(prec) :: nhat(1:3),nmag

    call gpuCheck(hipMemcpy(c_loc(this%solution%boundary), &
                            this%solution%boundary_gpu,sizeof(this%solution%boundary), &
                            hipMemcpyDeviceToHost))

    call gpuCheck(hipMemcpy(c_loc(this%solution%extboundary), &
                            this%solution%extboundary_gpu,sizeof(this%solution%extboundary), &
                            hipMemcpyDeviceToHost))

    call gpuCheck(hipMemcpy(c_loc(this%solutiongradient%avgboundary), &
                            this%solutiongradient%avgboundary_gpu,sizeof(this%solutiongradient%avgboundary), &
                            hipMemcpyDeviceToHost))
    do iEl = 1,this%solution%nElem
      do k = 1,6
        do j = 1,this%solution%interp%N+1
          do i = 1,this%solution%interp%N+1
            ! Get the boundary normals on cell edges from the mesh geometry
            nhat = this%geometry%nHat%boundary(i,j,k,iEl,1,1:3)
            sL = this%solution%boundary(i,j,k,iel,1:this%nvar) ! interior solution
            sR = this%solution%extboundary(i,j,k,iel,1:this%nvar) ! exterior solution
            dsdx = this%solutiongradient%avgboundary(i,j,k,iel,1:this%nvar,1:3)
            nmag = this%geometry%nScale%boundary(i,j,k,iEl,1)

            this%flux%boundaryNormal(i,j,k,iEl,1:this%nvar) = this%riemannflux3d(sL,sR,dsdx,nhat)*nmag
          enddo
        enddo
      enddo
    enddo

    call gpuCheck(hipMemcpy(this%flux%boundarynormal_gpu, &
                            c_loc(this%flux%boundarynormal), &
                            sizeof(this%flux%boundarynormal), &
                            hipMemcpyHostToDevice))

  endsubroutine BoundaryFlux_DGModel3D