“…Discrete ordinate-matrix exponential approach. To simplify the exposition, wc deal only with the zero-order Fourier component or the azimuthally averaged version of equation (6) Wiscombe [1976Wiscombe [ , 1983 for references). These methods or slight variants thereof are also referred to as discrete space theory [Preisendorfer, 1965;Stephens, 1980] ,,,,-: ,,,,,,-:,-,,, r,-, -,,,,',',-'…”