model_init Function

    function model_init(array, func, kopt) result(out)
        !! Initalise the model type.
        type(model) :: out

        !> Operator to apply to SDF.
        procedure(op) :: func
        !> Array of SDFs
        type(sdf),               intent(IN) :: array(:)
        !> Parameter used in modifier
        real(kind=wp), optional, intent(IN) :: kopt

        integer :: i

        out%array = array

        out%func => func
        if(present(kopt))then
            out%k = kopt
        else
            out%k = 0._wp
        end if

        do i = 2, size(array)
            if(array(1)%value%optProps%value%mus /= array(i)%value%optProps%value%mus)then
                print*,"Error mismatch in model mus in object: ",i
            end if
            if(array(1)%value%optProps%value%mua /= array(i)%value%optProps%value%mua)then
                print*,"Error mismatch in model mua in object: ",i
            end if
            if(array(1)%value%optProps%value%hgg /= array(i)%value%optProps%value%hgg)then
                print*,"Error mismatch in model hgg in object: ",i
            end if
            if(array(1)%value%optProps%value%n /= array(i)%value%optProps%value%n)then
                print*,"Error mismatch in model n in object: ",i
            end if
            if(array(1)%value%layer /= array(i)%value%layer)then
                print*,"Error mismatch in model layer in object: ",i
            end if
        end do

            out%optProps = array(1)%value%optProps
            out%layer = array(1)%value%layer

    end function model_init