get_partial_squared_val_sum Subroutine

  pure subroutine get_partial_squared_val_sum(this, upstream_grad, output)
    !! Fused partial+sum for squared: output(:,1) = sum_s(upstream * left_op * 2)
    implicit none
    class(array_type), intent(in) :: this
    real(real32), dimension(:,:), intent(in) :: upstream_grad
    real(real32), dimension(:), intent(out) :: output

    integer :: s, n_samples

    n_samples = size(upstream_grad, 2)
    if(.not.this%left_operand%is_sample_dependent)then
       output(:) = upstream_grad(:,1)
       do s = 2, n_samples
          output(:) = output(:) + upstream_grad(:,s)
       end do
       output(:) = output(:) * this%left_operand%val(:,1) * 2._real32
    else
       output(:) = upstream_grad(:,1) * this%left_operand%val(:,1) * 2._real32
       do s = 2, n_samples
          output(:) = output(:) + &
               upstream_grad(:,s) * this%left_operand%val(:,s) * 2._real32
       end do
    end if
  end subroutine get_partial_squared_val_sum