C***********************************************************************
C
C Subroutine BHCOAT calculates Q_ext, Q_sca, Q_back for coated sphere.
C All bessel functions computed by upward recurrence.
C Input:
C        X = 2*PI*RCORE*REFMED/WAVEL
C        Y = 2*PI*RMANT*REFMED/WAVEL
C        RFREL1 = REFCOR/REFMED
C        RFREL2 = REFMAN/REFMED 
C where  REFCOR = complex refr.index of core)
C        REFMAN = complex refr.index of mantle)
C        REFMED = real refr.index of medium)
C        RCORE = radius of core
C        RMANT = radius of mantle
C        WAVEL = wavelength of light in ambient medium
C
C Routine BHCOAT is taken from Bohren & Huffman (1983)
C Obtained from C.L.Joseph
C
C History:
C 92/11/24 (BTD) Explicit declaration of all variables
C***********************************************************************

