St-Maxwell

!> ccgk: This code generates Lebedev grids. It is based on C files from
!> ccgk: Dmitri Laikov, which were converted to FORTRAN by Christoph van Wuellen.
!> ccgk: I (Gerald Knizia) subsequently converted them back to C++.
!> ccsm: The Fortran90 version was converted by St Maxwell from C++ version.
!> ccgk:
!> ccgk: The original distribution contained the following readme file:
!> ccgk:
!>       Lebedev grids of orders n=6m+5 where m=0,1,...,21 in 16 digit precision
!>       =======================================================================
!> 

St-Maxwell

!> reference: https://github.com/KT19/automatic_differentiation
module backward
    use iso_fortran_env, only: real64
    implicit none

    type :: node
        private
        real(kind=real64) :: val
        real(kind=real64) :: grad = 0._real64
        type(pair), dimension(:), pointer :: parents