get_partial_softmax_reverse_left_val Subroutine

  pure subroutine get_partial_softmax_reverse_left_val(this, upstream_grad, output)
    !! Get partial derivative of softmax reverse operation (in-place version)
    implicit none
    class(array_type), intent(in) :: this
    real(real32), dimension(:,:), intent(in) :: upstream_grad
    real(real32), dimension(:,:), intent(out) :: output

    integer :: dim, i
    real(real32), dimension(size(this%val,3-this%indices(1))) :: sum_yg
    real(real32), dimension(size(this%val,3-this%indices(1))) :: sum_yu

    dim = this%indices(1)
    sum_yg = sum(this%left_operand%val * this%right_operand%val, dim=dim)
    sum_yu = sum(this%left_operand%val * upstream_grad, dim=dim)

    if(dim.eq.1)then
       do concurrent(i=1:size(this%val,2))
          output(:, i) = &
               upstream_grad(:, i) * (this%right_operand%val(:, i) - sum_yg(i)) - &
               this%right_operand%val(:, i) * sum_yu(i)
       end do
    else
       do concurrent(i=1:size(this%val,1))
          output(i, :) = &
               upstream_grad(i, :) * (this%right_operand%val(i, :) - sum_yg(i)) - &
               this%right_operand%val(i, :) * sum_yu(i)
       end do
    end if

  end subroutine get_partial_softmax_reverse_left_val