Wigner Symbols

Wigner, Clebsch-Gordan, Racah, and Gaunt coefficients

Collection of functions for calculating Wigner 3j, 6j, 9j, Clebsch-Gordan, Racah as well as Gaunt coefficients exactly, all evaluating to a rational number times the square root of a rational number [Rasch03].

Please see the description of the individual functions for further details and examples.

References

Rasch03(1,2,3,4,5,6)

J. Rasch and A. C. H. Yu, ‘Efficient Storage Scheme for Pre-calculated Wigner 3j, 6j and Gaunt Coefficients’, SIAM J. Sci. Comput. Volume 25, Issue 4, pp. 1416-1428 (2003)

Credits and Copyright

This code was taken from Sage with the permission of all authors:

https://groups.google.com/forum/#!topic/sage-devel/M4NZdu-7O38

AUTHORS:

• Jens Rasch (2009-03-24): initial version for Sage

• Jens Rasch (2009-05-31): updated to sage-4.0

Copyright (C) 2008 Jens Rasch <jyr2000@gmail.com>

class sympy.physics.wigner.Wigner3j(*args)

doit(**hints)

Evaluate objects that are not evaluated by default like limits, integrals, sums and products. All objects of this kind will be evaluated recursively, unless some species were excluded via ‘hints’ or unless the ‘deep’ hint was set to ‘False’.

>>> from sympy import Integral
>>> from sympy.abc import x

>>> 2*Integral(x, x)
2*Integral(x, x)

>>> (2*Integral(x, x)).doit()
x**2

>>> (2*Integral(x, x)).doit(deep=False)
2*Integral(x, x)

sympy.physics.wigner.clebsch_gordan(j_1, j_2, j_3, m_1, m_2, m_3)

Calculates the Clebsch-Gordan coefficient \(\langle j_1 m_1 \; j_2 m_2 | j_3 m_3 \rangle\).

The reference for this function is [Edmonds74].

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 import S
>>> from sympy.physics.wigner import clebsch_gordan
>>> clebsch_gordan(S(3)/2, S(1)/2, 2, S(3)/2, S(1)/2, 2)
1
>>> clebsch_gordan(S(3)/2, S(1)/2, 1, S(3)/2, -S(1)/2, 1)
sqrt(3)/2
>>> clebsch_gordan(S(3)/2, S(1)/2, 1, -S(1)/2, S(1)/2, 0)
-sqrt(2)/2

NOTES:

The Clebsch-Gordan coefficient will be evaluated via its relation to Wigner 3j symbols:

\[\langle j_1 m_1 \; j_2 m_2 | j_3 m_3 \rangle =(-1)^{j_1-j_2+m_3} \sqrt{2j_3+1} \operatorname{Wigner3j}(j_1,j_2,j_3,m_1,m_2,-m_3)\]

See also the documentation on Wigner 3j symbols which exhibit much higher symmetry relations than the Clebsch-Gordan coefficient.

AUTHORS:

• Jens Rasch (2009-03-24): initial version

sympy.physics.wigner.dot_rot_grad_Ynm(j, p, l, m, theta, phi)

Returns dot product of rotational gradients of spherical harmonics.

This function returns the right hand side of the following expression:

\[\vec{R}Y{_j^{p}} \cdot \vec{R}Y{_l^{m}} = (-1)^{m+p} \sum\limits_{k=|l-j|}^{l+j}Y{_k^{m+p}} * \alpha_{l,m,j,p,k} * \frac{1}{2} (k^2-j^2-l^2+k-j-l)\]

Arguments

j, p, l, m …. indices in spherical harmonics (expressions or integers) theta, phi …. angle arguments in spherical harmonics

Example

>>> from sympy import symbols
>>> from sympy.physics.wigner import dot_rot_grad_Ynm
>>> theta, phi = symbols("theta phi")
>>> dot_rot_grad_Ynm(3, 2, 2, 0, theta, phi).doit()
3*sqrt(55)*Ynm(5, 2, theta, phi)/(11*sqrt(pi))

sympy.physics.wigner.gaunt(l_1, l_2, l_3, m_1, m_2, m_3, prec=None)

Calculate the Gaunt coefficient.

The Gaunt coefficient is defined as the integral over three spherical harmonics:

\[\begin{split}\begin{aligned} \operatorname{Gaunt}(l_1,l_2,l_3,m_1,m_2,m_3) &=\int Y_{l_1,m_1}(\Omega) Y_{l_2,m_2}(\Omega) Y_{l_3,m_3}(\Omega) \,d\Omega \\ &=\sqrt{\frac{(2l_1+1)(2l_2+1)(2l_3+1)}{4\pi}} \operatorname{Wigner3j}(l_1,l_2,l_3,0,0,0) \operatorname{Wigner3j}(l_1,l_2,l_3,m_1,m_2,m_3) \end{aligned}\end{split}\]

INPUT:

• l_1, l_2, l_3, m_1, m_2, m_3 - integer

• prec - precision, default: None. Providing a precision can drastically speed up the calculation.

OUTPUT:

Rational number times the square root of a rational number (if prec=None), or real number if a precision is given.

Examples

>>> from sympy.physics.wigner import gaunt
>>> gaunt(1,0,1,1,0,-1)
-1/(2*sqrt(pi))
>>> gaunt(1000,1000,1200,9,3,-12).n(64)
0.00689500421922113448...

It is an error to use non-integer values for \(l\) and \(m\):

sage: gaunt(1.2,0,1.2,0,0,0)
Traceback (most recent call last):
...
ValueError: l values must be integer
sage: gaunt(1,0,1,1.1,0,-1.1)
Traceback (most recent call last):
...
ValueError: m values must be integer

NOTES:

The Gaunt coefficient obeys the following symmetry rules:

• invariant under any permutation of the columns

  \[\begin{split}\begin{aligned} Y(l_1,l_2,l_3,m_1,m_2,m_3) &=Y(l_3,l_1,l_2,m_3,m_1,m_2) \\ &=Y(l_2,l_3,l_1,m_2,m_3,m_1) \\ &=Y(l_3,l_2,l_1,m_3,m_2,m_1) \\ &=Y(l_1,l_3,l_2,m_1,m_3,m_2) \\ &=Y(l_2,l_1,l_3,m_2,m_1,m_3) \end{aligned}\end{split}\]

• invariant under space inflection, i.e.

  \[Y(l_1,l_2,l_3,m_1,m_2,m_3) =Y(l_1,l_2,l_3,-m_1,-m_2,-m_3)\]

• symmetric with respect to the 72 Regge symmetries as inherited for the \(3j\) symbols [Regge58]

• zero for \(l_1\), \(l_2\), \(l_3\) not fulfilling triangle relation

• zero for violating any one of the conditions: \(l_1 \ge |m_1|\), \(l_2 \ge |m_2|\), \(l_3 \ge |m_3|\)

• non-zero only for an even sum of the \(l_i\), i.e. \(L = l_1 + l_2 + l_3 = 2n\) for \(n\) in \(\mathbb{N}\)

ALGORITHM:

This function uses the algorithm of [Liberatodebrito82] to calculate the value of the Gaunt coefficient 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:

Liberatodebrito82

‘FORTRAN program for the integral of three spherical harmonics’, A. Liberato de Brito, Comput. Phys. Commun., Volume 25, pp. 81-85 (1982)

AUTHORS:

• Jens Rasch (2009-03-24): initial version for Sage

sympy.physics.wigner.racah(aa, bb, cc, dd, ee, ff, prec=None)

Calculate the Racah symbol \(W(a,b,c,d;e,f)\).

INPUT:

• a, …, f - integer or half integer

• prec - precision, default: None. Providing a precision can drastically speed up the calculation.

OUTPUT:

Rational number times the square root of a rational number (if prec=None), or real number if a precision is given.

Examples

>>> from sympy.physics.wigner import racah
>>> racah(3,3,3,3,3,3)
-1/14

NOTES:

The Racah symbol is related to the Wigner 6j symbol:

\[\operatorname{Wigner6j}(j_1,j_2,j_3,j_4,j_5,j_6) =(-1)^{j_1+j_2+j_4+j_5} W(j_1,j_2,j_5,j_4,j_3,j_6)\]

Please see the 6j symbol for its much richer symmetries and for additional properties.

ALGORITHM:

This function uses the algorithm of [Edmonds74] to calculate the value of the 6j 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].

AUTHORS:

• Jens Rasch (2009-03-24): initial version

sympy.physics.wigner.wigner_3j(j_1, j_2, j_3, m_1, m_2, m_3)

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 \(J:=j_1+j_2+j_3\)):

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

• invariant under space inflection, i.e.

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

• 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(1,2)

‘Symmetry Properties of Clebsch-Gordan Coefficients’, T. Regge, Nuovo Cimento, Volume 10, pp. 544 (1958)

Edmonds74(1,2,3,4,5)

‘Angular Momentum in Quantum Mechanics’, A. R. Edmonds, Princeton University Press (1974)

AUTHORS:

• Jens Rasch (2009-03-24): initial version

sympy.physics.wigner.wigner_6j(j_1, j_2, j_3, j_4, j_5, j_6, prec=None)

Calculate the Wigner 6j symbol \(\operatorname{Wigner6j}(j_1,j_2,j_3,j_4,j_5,j_6)\).

INPUT:

• j_1, …, j_6 - integer or half integer

• prec - precision, default: None. Providing a precision can drastically speed up the calculation.

OUTPUT:

Rational number times the square root of a rational number (if prec=None), or real number if a precision is given.

Examples

>>> from sympy.physics.wigner import wigner_6j
>>> wigner_6j(3,3,3,3,3,3)
-1/14
>>> wigner_6j(5,5,5,5,5,5)
1/52

It is an error to have arguments that are not integer or half integer values or do not fulfill the triangle relation:

sage: wigner_6j(2.5,2.5,2.5,2.5,2.5,2.5)
Traceback (most recent call last):
...
ValueError: j values must be integer or half integer and fulfill the triangle relation
sage: wigner_6j(0.5,0.5,1.1,0.5,0.5,1.1)
Traceback (most recent call last):
...
ValueError: j values must be integer or half integer and fulfill the triangle relation

NOTES:

The Wigner 6j symbol is related to the Racah symbol but exhibits more symmetries as detailed below.

\[\operatorname{Wigner6j}(j_1,j_2,j_3,j_4,j_5,j_6) =(-1)^{j_1+j_2+j_4+j_5} W(j_1,j_2,j_5,j_4,j_3,j_6)\]

The Wigner 6j symbol obeys the following symmetry rules:

• Wigner 6j symbols are left invariant under any permutation of the columns:

  \[\begin{split}\begin{aligned} \operatorname{Wigner6j}(j_1,j_2,j_3,j_4,j_5,j_6) &=\operatorname{Wigner6j}(j_3,j_1,j_2,j_6,j_4,j_5) \\ &=\operatorname{Wigner6j}(j_2,j_3,j_1,j_5,j_6,j_4) \\ &=\operatorname{Wigner6j}(j_3,j_2,j_1,j_6,j_5,j_4) \\ &=\operatorname{Wigner6j}(j_1,j_3,j_2,j_4,j_6,j_5) \\ &=\operatorname{Wigner6j}(j_2,j_1,j_3,j_5,j_4,j_6) \end{aligned}\end{split}\]

• They are invariant under the exchange of the upper and lower arguments in each of any two columns, i.e.

  \[\operatorname{Wigner6j}(j_1,j_2,j_3,j_4,j_5,j_6) =\operatorname{Wigner6j}(j_1,j_5,j_6,j_4,j_2,j_3) =\operatorname{Wigner6j}(j_4,j_2,j_6,j_1,j_5,j_3) =\operatorname{Wigner6j}(j_4,j_5,j_3,j_1,j_2,j_6)\]

• additional 6 symmetries [Regge59] giving rise to 144 symmetries in total

• only non-zero if any triple of \(j\)’s fulfill a triangle relation

ALGORITHM:

This function uses the algorithm of [Edmonds74] to calculate the value of the 6j 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:

Regge59

‘Symmetry Properties of Racah Coefficients’, T. Regge, Nuovo Cimento, Volume 11, pp. 116 (1959)

sympy.physics.wigner.wigner_9j(j_1, j_2, j_3, j_4, j_5, j_6, j_7, j_8, j_9, prec=None)

Calculate the Wigner 9j symbol \(\operatorname{Wigner9j}(j_1,j_2,j_3,j_4,j_5,j_6,j_7,j_8,j_9)\).

INPUT:

• j_1, …, j_9 - integer or half integer

• prec - precision, default: None. Providing a precision can drastically speed up the calculation.

OUTPUT:

Rational number times the square root of a rational number (if prec=None), or real number if a precision is given.

Examples

>>> from sympy.physics.wigner import wigner_9j
>>> wigner_9j(1,1,1, 1,1,1, 1,1,0 ,prec=64) # ==1/18
0.05555555...

It is an error to have arguments that are not integer or half integer values or do not fulfill the triangle relation:

sage: wigner_9j(0.5,0.5,0.5, 0.5,0.5,0.5, 0.5,0.5,0.5,prec=64)
Traceback (most recent call last):
...
ValueError: j values must be integer or half integer and fulfill the triangle relation
sage: wigner_9j(1,1,1, 0.5,1,1.5, 0.5,1,2.5,prec=64)
Traceback (most recent call last):
...
ValueError: j values must be integer or half integer and fulfill the triangle relation

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].