get_partial_softmax Function

  function get_partial_softmax(this, upstream_grad) result(output)
    !! Get partial derivative of softmax activation
    implicit none
    class(array_type), intent(inout) :: this
    type(array_type), intent(in) :: upstream_grad
    type(array_type) :: output
    type(array_type), pointer :: ptr

    integer :: dim

    if(this%indices(1).eq.1)then
       dim = 2
    else
       dim = 1
    end if
    ! ptr => this * upstream_grad
    ! ptr => ptr - this * sum(ptr, dim=dim)
    ptr => softmax_reverse_array(this, upstream_grad, this%indices(1))
    call output%assign_and_deallocate_source(ptr)

  end function get_partial_softmax