add_learnable Module Function

  module function add_learnable(a, b) result(output)
    !! Add two learnable layers together
    implicit none

    ! Arguments
    class(learnable_layer_type), intent(in) :: a, b
    !! Instances of layers
    class(learnable_layer_type), allocatable :: output
    !! Output layer

    ! Local variables
    integer :: i
    !! Loop index

    output = a
    if(allocated(a%params).and.allocated(b%params))then
       if(size(a%params).ne.size(b%params))then
          call stop_program("add_learnable: incompatible parameter sizes")
          return
       end if
       do i = 1, size(a%params,1)
          output%params(i)%grad => null()
          output%params(i) = a%params(i) + b%params(i)
          if(associated(a%params(i)%grad).and.&
               associated(b%params(i)%grad))then
             allocate(output%params(i)%grad)
             output%params(i)%grad = a%params(i)%grad + &
                  b%params(i)%grad
          end if
       end do
    else
       call stop_program("add_learnable: unallocated parameter arrays")
       return
    end if

  end function add_learnable