def wigner_3j(j_1, j_2, j_3, m_1, m_2, m_3):
    r"""
    Calculate the Wigner 3j symbol `\operatorname{Wigner3j}(j_1,j_2,j_3,m_1,m_2,m_3)`.

    INPUT:

    -  ``j_1``, ``j_2``, ``j_3``, ``m_1``, ``m_2``, ``m_3`` - integer or half integer

    OUTPUT:

    Rational number times the square root of a rational number.

    Examples
    ========

    >>> from sympy.physics.wigner import wigner_3j
    >>> wigner_3j(2, 6, 4, 0, 0, 0)
    sqrt(715)/143
    >>> wigner_3j(2, 6, 4, 0, 0, 1)
    0

    It is an error to have arguments that are not integer or half
    integer values::

        sage: wigner_3j(2.1, 6, 4, 0, 0, 0)
        Traceback (most recent call last):
        ...
        ValueError: j values must be integer or half integer
        sage: wigner_3j(2, 6, 4, 1, 0, -1.1)
        Traceback (most recent call last):
        ...
        ValueError: m values must be integer or half integer

    NOTES:

    The Wigner 3j symbol obeys the following symmetry rules:

    - invariant under any permutation of the columns (with the
      exception of a sign change where `J:=j_1+j_2+j_3`):

      .. math::

         \begin{aligned}
         \operatorname{Wigner3j}(j_1,j_2,j_3,m_1,m_2,m_3)
          &=\operatorname{Wigner3j}(j_3,j_1,j_2,m_3,m_1,m_2) \\
          &=\operatorname{Wigner3j}(j_2,j_3,j_1,m_2,m_3,m_1) \\
          &=(-1)^J \operatorname{Wigner3j}(j_3,j_2,j_1,m_3,m_2,m_1) \\
          &=(-1)^J \operatorname{Wigner3j}(j_1,j_3,j_2,m_1,m_3,m_2) \\
          &=(-1)^J \operatorname{Wigner3j}(j_2,j_1,j_3,m_2,m_1,m_3)
         \end{aligned}

    - invariant under space inflection, i.e.

      .. math::

         \operatorname{Wigner3j}(j_1,j_2,j_3,m_1,m_2,m_3)
         =(-1)^J \operatorname{Wigner3j}(j_1,j_2,j_3,-m_1,-m_2,-m_3)

    - symmetric with respect to the 72 additional symmetries based on
      the work by [Regge58]_

    - zero for `j_1`, `j_2`, `j_3` not fulfilling triangle relation

    - zero for `m_1 + m_2 + m_3 \neq 0`

    - zero for violating any one of the conditions
      `j_1 \ge |m_1|`,  `j_2 \ge |m_2|`,  `j_3 \ge |m_3|`

    ALGORITHM:

    This function uses the algorithm of [Edmonds74]_ to calculate the
    value of the 3j symbol exactly. Note that the formula contains
    alternating sums over large factorials and is therefore unsuitable
    for finite precision arithmetic and only useful for a computer
    algebra system [Rasch03]_.

    REFERENCES:

    .. [Regge58] 'Symmetry Properties of Clebsch-Gordan Coefficients',
      T. Regge, Nuovo Cimento, Volume 10, pp. 544 (1958)

    .. [Edmonds74] 'Angular Momentum in Quantum Mechanics',
      A. R. Edmonds, Princeton University Press (1974)

    AUTHORS:

    - Jens Rasch (2009-03-24): initial version
    """
    if int(j_1 * 2) != j_1 * 2 or int(j_2 * 2) != j_2 * 2 or \
            int(j_3 * 2) != j_3 * 2:
        raise ValueError("j values must be integer or half integer")
    if int(m_1 * 2) != m_1 * 2 or int(m_2 * 2) != m_2 * 2 or \
            int(m_3 * 2) != m_3 * 2:
        raise ValueError("m values must be integer or half integer")
    if m_1 + m_2 + m_3 != 0:
        return 0
    prefid = Integer((-1) ** int(j_1 - j_2 - m_3))
    m_3 = -m_3
    a1 = j_1 + j_2 - j_3
    if a1 < 0:
        return 0
    a2 = j_1 - j_2 + j_3
    if a2 < 0:
        return 0
    a3 = -j_1 + j_2 + j_3
    if a3 < 0:
        return 0
    if (abs(m_1) > j_1) or (abs(m_2) > j_2) or (abs(m_3) > j_3):
        return 0

    maxfact = max(j_1 + j_2 + j_3 + 1, j_1 + abs(m_1), j_2 + abs(m_2),
                  j_3 + abs(m_3))
    _calc_factlist(int(maxfact))

    argsqrt = Integer(_Factlist[int(j_1 + j_2 - j_3)] *
                     _Factlist[int(j_1 - j_2 + j_3)] *
                     _Factlist[int(-j_1 + j_2 + j_3)] *
                     _Factlist[int(j_1 - m_1)] *
                     _Factlist[int(j_1 + m_1)] *
                     _Factlist[int(j_2 - m_2)] *
                     _Factlist[int(j_2 + m_2)] *
                     _Factlist[int(j_3 - m_3)] *
                     _Factlist[int(j_3 + m_3)]) / \
        _Factlist[int(j_1 + j_2 + j_3 + 1)]

    ressqrt = sqrt(argsqrt)
    if ressqrt.is_complex:
        ressqrt = ressqrt.as_real_imag()[0]

    imin = max(-j_3 + j_1 + m_2, -j_3 + j_2 - m_1, 0)
    imax = min(j_2 + m_2, j_1 - m_1, j_1 + j_2 - j_3)
    sumres = 0
    for ii in range(int(imin), int(imax) + 1):
        den = _Factlist[ii] * \
            _Factlist[int(ii + j_3 - j_1 - m_2)] * \
            _Factlist[int(j_2 + m_2 - ii)] * \
            _Factlist[int(j_1 - ii - m_1)] * \
            _Factlist[int(ii + j_3 - j_2 + m_1)] * \
            _Factlist[int(j_1 + j_2 - j_3 - ii)]
        sumres = sumres + Integer((-1) ** ii) / den

    res = ressqrt * sumres * prefid
    return res
dataset/ETHPy150Open sympy/sympy/sympy/physics/wigner.py/wigner_3j/original