The Wigner 3-j, 6-j and 9-j symbols give the coupling coefficients for combined angular momentum vectors. Since the arguments of the standard coupling coefficient functions are integer or half-integer, the arguments of the following functions are, by convention, integers equal to twice the actual spin value. For information on the 3-j coefficients see Abramowitz & Stegun, Section 27.9.
These routines compute the Wigner 3-j coefficient,
where the arguments are given in half-integer units, ja = two_ja / 2, ma = two_ma / 2, etc.
These routines compute the Wigner 6-j coefficient,
where the arguments are given in half-integer units, ja = two_ja / 2, jb = two_jb / 2, etc.
These routines compute the Wigner 9-j coefficient,
where the arguments are given in half-integer units, ja = two_ja / 2, jb = two_jb / 2, etc.