— Function: double gsl_sf_coupling_6j (int two_ja, int two_jb, int two_jc, int two_jd, int two_je, int two_jf)
— Function: int gsl_sf_coupling_6j_e (int two_ja, int two_jb, int two_jc, int two_jd, int two_je, int two_jf, gsl_sf_result * result)

These routines compute the Wigner 6-j coefficient,

          {ja jb jc
           jd je jf}

where the arguments are given in half-integer units, ja = two_ja/2, ma = two_ma/2, etc.