Owl_base_complexSource``rect r phi`` return a complex number with polar coordinates ``r`` and ``phi``.
``to_tuple x`` converts a complex number to tuple ``(x.re; x.im)``.
``is_nan x`` returns ``true`` if ``x.re`` is ``nan`` or ``x.im`` is ``nan``.
``is_inf x`` returns ``true`` if either ``x.re`` or ``x.im`` is ``infinity`` or ``neg_infinity``.