apply_selu Function

  function apply_selu(this, val) result(output)
    !! Apply SELU activation to array
    !!
    !! Computes: f(x) = λ * x if x > 0
    !!           f(x) = λ * α * (exp(x) - 1) if x ≤ 0
    implicit none

    ! Arguments
    class(selu_actv_type), intent(in) :: this
    !! SELU activation type
    type(array_type), intent(in) :: val
    !! Input values
    type(array_type), pointer :: output
    !! Activated output values

    ! Local variables
    type(array_type), pointer :: positive_part, negative_part

    ! Compute SELU: λ * merge(x, α * (exp(x) - 1), x > 0)
    positive_part => val * this%lambda
    negative_part => (exp(val) - 1._real32) * this%alpha * this%lambda
    output => merge(positive_part, negative_part, val .gt. 0._real32)

    if(this%apply_scaling)then
       output => output * this%scale
    end if

  end function apply_selu