Power sum symmetric functions¶
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class
sage.combinat.sf.powersum.
SymmetricFunctionAlgebra_power
(Sym)¶ Bases:
sage.combinat.sf.multiplicative.SymmetricFunctionAlgebra_multiplicative
A class for methods associated to the power sum basis of the symmetric functions
INPUT:
self
– the power sum basis of the symmetric functionsSym
– an instance of the ring of symmetric functions
TESTS:
sage: p = SymmetricFunctions(QQ).p() sage: p == loads(dumps(p)) True sage: TestSuite(p).run(skip=['_test_associativity', '_test_distributivity', '_test_prod']) sage: TestSuite(p).run(elements = [p[1,1]+p[2], p[1]+2*p[1,1]])
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class
Element
(M, x)¶ Bases:
sage.combinat.sf.classical.SymmetricFunctionAlgebra_classical.Element
Create a combinatorial module element. This should never be called directly, but only through the parent combinatorial free module’s
__call__()
method.TESTS:
sage: F = CombinatorialFreeModule(QQ, ['a','b','c']) sage: B = F.basis() sage: f = B['a'] + 3*B['c']; f B['a'] + 3*B['c'] sage: f == loads(dumps(f)) True
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adams_operation
(n)¶ Return the image of the symmetric function
self
under the \(n\)-th Frobenius operator.The \(n\)-th Frobenius operator \(\mathbf{f}_n\) is defined to be the map from the ring of symmetric functions to itself that sends every symmetric function \(P(x_1, x_2, x_3, \ldots)\) to \(P(x_1^n, x_2^n, x_3^n, \ldots)\). This operator \(\mathbf{f}_n\) is a Hopf algebra endomorphism, and satisfies
\[\mathbf{f}_n m_{(\lambda_1, \lambda_2, \lambda_3, \ldots)} = m_{(n\lambda_1, n\lambda_2, n\lambda_3, \ldots)}\]for every partition \((\lambda_1, \lambda_2, \lambda_3, \ldots)\) (where \(m\) means the monomial basis). Moreover, \(\mathbf{f}_n (p_r) = p_{nr}\) for every positive integer \(r\) (where \(p_k\) denotes the \(k\)-th powersum symmetric function).
The \(n\)-th Frobenius operator is also called the \(n\)-th Frobenius endomorphism. It is not related to the Frobenius map which connects the ring of symmetric functions with the representation theory of the symmetric group.
The \(n\)-th Frobenius operator is also the \(n\)-th Adams operator of the \(\Lambda\)-ring of symmetric functions over the integers.
The \(n\)-th Frobenius operator can also be described via plethysm: Every symmetric function \(P\) satisfies \(\mathbf{f}_n(P) = p_n \circ P = P \circ p_n\), where \(p_n\) is the \(n\)-th powersum symmetric function, and \(\circ\) denotes (outer) plethysm.
INPUT:
n
– a positive integer
OUTPUT:
The result of applying the \(n\)-th Frobenius operator (on the ring of symmetric functions) to
self
.EXAMPLES:
sage: Sym = SymmetricFunctions(ZZ) sage: p = Sym.p() sage: p[3].frobenius(2) p[6] sage: p[4,2,1].frobenius(3) p[12, 6, 3] sage: p([]).frobenius(4) p[] sage: p[3].frobenius(1) p[3] sage: (p([3]) - p([2]) + p([])).frobenius(3) p[] - p[6] + p[9]
TESTS:
Let us check that this method on the powersum basis gives the same result as the implementation in
sage.combinat.sf.sfa
on the complete homogeneous basis:sage: Sym = SymmetricFunctions(QQ) sage: p = Sym.p(); h = Sym.h() sage: all( h(p(lam)).frobenius(3) == h(p(lam).frobenius(3)) ....: for lam in Partitions(3) ) True sage: all( p(h(lam)).frobenius(2) == p(h(lam).frobenius(2)) ....: for lam in Partitions(4) ) True
See also
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eval_at_permutation_roots
(rho)¶ Evaluate at eigenvalues of a permutation matrix.
Evaluate an element of the power sum basis at the eigenvalues of a permutation matrix with cycle structure \(\rho\).
This function evaluates an element at the roots of unity
\[\Xi_{\rho_1},\Xi_{\rho_2},\ldots,\Xi_{\rho_\ell}\]where
\[\Xi_{m} = 1,\zeta_m,\zeta_m^2,\ldots,\zeta_m^{m-1}\]and \(\zeta_m\) is an \(m\) root of unity. These roots of unity represent the eigenvalues of permutation matrix with cycle structure \(\rho\).
INPUT:
rho
– a partition or a list of non-negative integers
OUTPUT:
- an element of the base ring
EXAMPLES:
sage: p = SymmetricFunctions(QQ).p() sage: p([3,3]).eval_at_permutation_roots([6]) 0 sage: p([3,3]).eval_at_permutation_roots([3]) 9 sage: p([3,3]).eval_at_permutation_roots([1]) 1 sage: p([3,3]).eval_at_permutation_roots([3,3]) 36 sage: p([3,3]).eval_at_permutation_roots([1,1,1,1,1]) 25 sage: (p[1]+p[2]+p[3]).eval_at_permutation_roots([3,2]) 5
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expand
(n, alphabet='x')¶ Expand the symmetric function
self
as a symmetric polynomial inn
variables.INPUT:
n
– a nonnegative integeralphabet
– (default:'x'
) a variable for the expansion
OUTPUT:
A monomial expansion of
self
in the \(n\) variables labelled byalphabet
.EXAMPLES:
sage: p = SymmetricFunctions(QQ).p() sage: a = p([2]) sage: a.expand(2) x0^2 + x1^2 sage: a.expand(3, alphabet=['a','b','c']) a^2 + b^2 + c^2 sage: p([2,1,1]).expand(2) x0^4 + 2*x0^3*x1 + 2*x0^2*x1^2 + 2*x0*x1^3 + x1^4 sage: p([7]).expand(4) x0^7 + x1^7 + x2^7 + x3^7 sage: p([7]).expand(4,alphabet='t') t0^7 + t1^7 + t2^7 + t3^7 sage: p([7]).expand(4,alphabet='x,y,z,t') x^7 + y^7 + z^7 + t^7 sage: p(1).expand(4) 1 sage: p(0).expand(4) 0 sage: (p([]) + 2*p([1])).expand(3) 2*x0 + 2*x1 + 2*x2 + 1 sage: p([1]).expand(0) 0 sage: (3*p([])).expand(0) 3
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frobenius
(n)¶ Return the image of the symmetric function
self
under the \(n\)-th Frobenius operator.The \(n\)-th Frobenius operator \(\mathbf{f}_n\) is defined to be the map from the ring of symmetric functions to itself that sends every symmetric function \(P(x_1, x_2, x_3, \ldots)\) to \(P(x_1^n, x_2^n, x_3^n, \ldots)\). This operator \(\mathbf{f}_n\) is a Hopf algebra endomorphism, and satisfies
\[\mathbf{f}_n m_{(\lambda_1, \lambda_2, \lambda_3, \ldots)} = m_{(n\lambda_1, n\lambda_2, n\lambda_3, \ldots)}\]for every partition \((\lambda_1, \lambda_2, \lambda_3, \ldots)\) (where \(m\) means the monomial basis). Moreover, \(\mathbf{f}_n (p_r) = p_{nr}\) for every positive integer \(r\) (where \(p_k\) denotes the \(k\)-th powersum symmetric function).
The \(n\)-th Frobenius operator is also called the \(n\)-th Frobenius endomorphism. It is not related to the Frobenius map which connects the ring of symmetric functions with the representation theory of the symmetric group.
The \(n\)-th Frobenius operator is also the \(n\)-th Adams operator of the \(\Lambda\)-ring of symmetric functions over the integers.
The \(n\)-th Frobenius operator can also be described via plethysm: Every symmetric function \(P\) satisfies \(\mathbf{f}_n(P) = p_n \circ P = P \circ p_n\), where \(p_n\) is the \(n\)-th powersum symmetric function, and \(\circ\) denotes (outer) plethysm.
INPUT:
n
– a positive integer
OUTPUT:
The result of applying the \(n\)-th Frobenius operator (on the ring of symmetric functions) to
self
.EXAMPLES:
sage: Sym = SymmetricFunctions(ZZ) sage: p = Sym.p() sage: p[3].frobenius(2) p[6] sage: p[4,2,1].frobenius(3) p[12, 6, 3] sage: p([]).frobenius(4) p[] sage: p[3].frobenius(1) p[3] sage: (p([3]) - p([2]) + p([])).frobenius(3) p[] - p[6] + p[9]
TESTS:
Let us check that this method on the powersum basis gives the same result as the implementation in
sage.combinat.sf.sfa
on the complete homogeneous basis:sage: Sym = SymmetricFunctions(QQ) sage: p = Sym.p(); h = Sym.h() sage: all( h(p(lam)).frobenius(3) == h(p(lam).frobenius(3)) ....: for lam in Partitions(3) ) True sage: all( p(h(lam)).frobenius(2) == p(h(lam).frobenius(2)) ....: for lam in Partitions(4) ) True
See also
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omega
()¶ Return the image of
self
under the omega automorphism.The omega automorphism is defined to be the unique algebra endomorphism \(\omega\) of the ring of symmetric functions that satisfies \(\omega(e_k) = h_k\) for all positive integers \(k\) (where \(e_k\) stands for the \(k\)-th elementary symmetric function, and \(h_k\) stands for the \(k\)-th complete homogeneous symmetric function). It furthermore is a Hopf algebra endomorphism and an involution, and it is also known as the omega involution. It sends the power-sum symmetric function \(p_k\) to \((-1)^{k-1} p_k\) for every positive integer \(k\).
The images of some bases under the omega automorphism are given by
\[\omega(e_{\lambda}) = h_{\lambda}, \qquad \omega(h_{\lambda}) = e_{\lambda}, \qquad \omega(p_{\lambda}) = (-1)^{|\lambda| - \ell(\lambda)} p_{\lambda}, \qquad \omega(s_{\lambda}) = s_{\lambda^{\prime}},\]where \(\lambda\) is any partition, where \(\ell(\lambda)\) denotes the length (
length()
) of the partition \(\lambda\), where \(\lambda^{\prime}\) denotes the conjugate partition (conjugate()
) of \(\lambda\), and where the usual notations for bases are used (\(e\) = elementary, \(h\) = complete homogeneous, \(p\) = powersum, \(s\) = Schur).omega_involution()
is a synonym for theomega()
method.OUTPUT:
- the image of
self
under the omega automorphism
EXAMPLES:
sage: p = SymmetricFunctions(QQ).p() sage: a = p([2,1]); a p[2, 1] sage: a.omega() -p[2, 1] sage: p([]).omega() p[] sage: p(0).omega() 0 sage: p = SymmetricFunctions(ZZ).p() sage: (p([3,1,1]) - 2 * p([2,1])).omega() 2*p[2, 1] + p[3, 1, 1]
- the image of
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omega_involution
()¶ Return the image of
self
under the omega automorphism.The omega automorphism is defined to be the unique algebra endomorphism \(\omega\) of the ring of symmetric functions that satisfies \(\omega(e_k) = h_k\) for all positive integers \(k\) (where \(e_k\) stands for the \(k\)-th elementary symmetric function, and \(h_k\) stands for the \(k\)-th complete homogeneous symmetric function). It furthermore is a Hopf algebra endomorphism and an involution, and it is also known as the omega involution. It sends the power-sum symmetric function \(p_k\) to \((-1)^{k-1} p_k\) for every positive integer \(k\).
The images of some bases under the omega automorphism are given by
\[\omega(e_{\lambda}) = h_{\lambda}, \qquad \omega(h_{\lambda}) = e_{\lambda}, \qquad \omega(p_{\lambda}) = (-1)^{|\lambda| - \ell(\lambda)} p_{\lambda}, \qquad \omega(s_{\lambda}) = s_{\lambda^{\prime}},\]where \(\lambda\) is any partition, where \(\ell(\lambda)\) denotes the length (
length()
) of the partition \(\lambda\), where \(\lambda^{\prime}\) denotes the conjugate partition (conjugate()
) of \(\lambda\), and where the usual notations for bases are used (\(e\) = elementary, \(h\) = complete homogeneous, \(p\) = powersum, \(s\) = Schur).omega_involution()
is a synonym for theomega()
method.OUTPUT:
- the image of
self
under the omega automorphism
EXAMPLES:
sage: p = SymmetricFunctions(QQ).p() sage: a = p([2,1]); a p[2, 1] sage: a.omega() -p[2, 1] sage: p([]).omega() p[] sage: p(0).omega() 0 sage: p = SymmetricFunctions(ZZ).p() sage: (p([3,1,1]) - 2 * p([2,1])).omega() 2*p[2, 1] + p[3, 1, 1]
- the image of
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scalar
(x, zee=None)¶ Return the standard scalar product of
self
andx
.INPUT:
x
– a power sum symmetric functionzee
– (default: uses standardzee
function) optional input specifying the scalar product on the power sum basis with normalization \(\langle p_{\mu}, p_{\mu} \rangle = \mathrm{zee}(\mu)\).zee
should be a function on partitions.
Note that the power-sum symmetric functions are orthogonal under this scalar product. With the default value of
zee
, the value of \(\langle p_{\lambda}, p_{\lambda} \rangle\) is given by the size of the centralizer in \(S_n\) of a permutation of cycle type \(\lambda\).OUTPUT:
- the standard scalar product between
self
andx
, or, if the optional parameterzee
is specified, then the scalar product with respect to the normalization \(\langle p_{\mu}, p_{\mu} \rangle = \mathrm{zee}(\mu)\) with the power sum basis elements being orthogonal
EXAMPLES:
sage: p = SymmetricFunctions(QQ).p() sage: p4 = Partitions(4) sage: matrix([ [p(a).scalar(p(b)) for a in p4] for b in p4]) [ 4 0 0 0 0] [ 0 3 0 0 0] [ 0 0 8 0 0] [ 0 0 0 4 0] [ 0 0 0 0 24] sage: p(0).scalar(p(1)) 0 sage: p(1).scalar(p(2)) 2 sage: zee = lambda x : 1 sage: matrix( [[p[la].scalar(p[mu], zee) for la in Partitions(3)] for mu in Partitions(3)]) [1 0 0] [0 1 0] [0 0 1]
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verschiebung
(n)¶ Return the image of the symmetric function
self
under the \(n\)-th Verschiebung operator.The \(n\)-th Verschiebung operator \(\mathbf{V}_n\) is defined to be the unique algebra endomorphism \(V\) of the ring of symmetric functions that satisfies \(V(h_r) = h_{r/n}\) for every positive integer \(r\) divisible by \(n\), and satisfies \(V(h_r) = 0\) for every positive integer \(r\) not divisible by \(n\). This operator \(\mathbf{V}_n\) is a Hopf algebra endomorphism. For every nonnegative integer \(r\) with \(n \mid r\), it satisfies
\[\mathbf{V}_n(h_r) = h_{r/n}, \quad \mathbf{V}_n(p_r) = n p_{r/n}, \quad \mathbf{V}_n(e_r) = (-1)^{r - r/n} e_{r/n}\](where \(h\) is the complete homogeneous basis, \(p\) is the powersum basis, and \(e\) is the elementary basis). For every nonnegative integer \(r\) with \(n \nmid r\), it satisfes
\[\mathbf{V}_n(h_r) = \mathbf{V}_n(p_r) = \mathbf{V}_n(e_r) = 0.\]The \(n\)-th Verschiebung operator is also called the \(n\)-th Verschiebung endomorphism. Its name derives from the Verschiebung (German for “shift”) endomorphism of the Witt vectors.
The \(n\)-th Verschiebung operator is adjoint to the \(n\)-th Frobenius operator (see
frobenius()
for its definition) with respect to the Hall scalar product (scalar()
).The action of the \(n\)-th Verschiebung operator on the Schur basis can also be computed explicitly. The following (probably clumsier than necessary) description can be obtained by solving exercise 7.61 in Stanley’s [STA].
Let \(\lambda\) be a partition. Let \(n\) be a positive integer. If the \(n\)-core of \(\lambda\) is nonempty, then \(\mathbf{V}_n(s_\lambda) = 0\). Otherwise, the following method computes \(\mathbf{V}_n(s_\lambda)\): Write the partition \(\lambda\) in the form \((\lambda_1, \lambda_2, \ldots, \lambda_{ns})\) for some nonnegative integer \(s\). (If \(n\) does not divide the length of \(\lambda\), then this is achieved by adding trailing zeroes to \(\lambda\).) Set \(\beta_i = \lambda_i + ns - i\) for every \(s \in \{ 1, 2, \ldots, ns \}\). Then, \((\beta_1, \beta_2, \ldots, \beta_{ns})\) is a strictly decreasing sequence of nonnegative integers. Stably sort the list \((1, 2, \ldots, ns)\) in order of (weakly) increasing remainder of \(-1 - \beta_i\) modulo \(n\). Let \(\xi\) be the sign of the permutation that is used for this sorting. Let \(\psi\) be the sign of the permutation that is used to stably sort the list \((1, 2, \ldots, ns)\) in order of (weakly) increasing remainder of \(i - 1\) modulo \(n\). (Notice that \(\psi = (-1)^{n(n-1)s(s-1)/4}\).) Then, \(\mathbf{V}_n(s_\lambda) = \xi \psi \prod_{i = 0}^{n - 1} s_{\lambda^{(i)}}\), where \((\lambda^{(0)}, \lambda^{(1)}, \ldots, \lambda^{(n - 1)})\) is the \(n\)-quotient of \(\lambda\).
INPUT:
n
– a positive integer
OUTPUT:
The result of applying the \(n\)-th Verschiebung operator (on the ring of symmetric functions) to
self
.EXAMPLES:
sage: Sym = SymmetricFunctions(ZZ) sage: p = Sym.p() sage: p[3].verschiebung(2) 0 sage: p[4].verschiebung(4) 4*p[1]
The Verschiebung endomorphisms are multiplicative:
sage: all( all( p(lam).verschiebung(2) * p(mu).verschiebung(2) ....: == (p(lam) * p(mu)).verschiebung(2) ....: for mu in Partitions(4) ) ....: for lam in Partitions(4) ) True
Testing the adjointness between the Frobenius operators \(\mathbf{f}_n\) and the Verschiebung operators \(\mathbf{V}_n\):
sage: Sym = SymmetricFunctions(QQ) sage: p = Sym.p() sage: all( all( p(lam).verschiebung(2).scalar(p(mu)) ....: == p(lam).scalar(p(mu).frobenius(2)) ....: for mu in Partitions(2) ) ....: for lam in Partitions(4) ) True
TESTS:
Let us check that this method on the powersum basis gives the same result as the implementation in
sage.combinat.sf.sfa
on the monomial basis:sage: Sym = SymmetricFunctions(QQ) sage: p = Sym.p(); m = Sym.m() sage: all( m(p(lam)).verschiebung(3) == m(p(lam).verschiebung(3)) ....: for lam in Partitions(6) ) True sage: all( p(m(lam)).verschiebung(2) == p(m(lam).verschiebung(2)) ....: for lam in Partitions(4) ) True
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SymmetricFunctionAlgebra_power.
antipode_on_basis
(partition)¶ Return the antipode of
self[partition]
.The antipode on the generator \(p_i\) (for \(i > 0\)) is \(-p_i\), and the antipode on \(p_\mu\) is \((-1)^{length(\mu)} p_\mu\).
INPUT:
self
– the power sum basis of the symmetric functionspartition
– a partition
OUTPUT:
- the result of the antipode on
self(partition)
EXAMPLES:
sage: Sym = SymmetricFunctions(QQ) sage: p = Sym.p() sage: p.antipode_on_basis([2]) -p[2] sage: p.antipode_on_basis([3]) -p[3] sage: p.antipode_on_basis([2,2]) p[2, 2] sage: p.antipode_on_basis([]) p[]
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SymmetricFunctionAlgebra_power.
bottom_schur_function
(partition, degree=None)¶ Return the least-degree component of
s[partition]
, wheres
denotes the Schur basis of the symmetric functions, and the grading is not the usual grading on the symmetric functions but rather the grading which gives every \(p_i\) degree \(1\).This least-degree component has its degree equal to the Frobenius rank of
partition
, while the degree with respect to the usual grading is still the size ofpartition
.This method requires the base ring to be a (commutative) \(\QQ\)-algebra. This restriction is unavoidable, since the least-degree component (in general) has noninteger coefficients in all classical bases of the symmetric functions.
The optional keyword
degree
allows taking any homogeneous component rather than merely the least-degree one. Specifically, ifdegree
is set, then thedegree
-th component will be returned.REFERENCES:
[ClSt03] Peter Clifford, Richard P. Stanley, Bottom Schur functions. Arxiv math/0311382v2. EXAMPLES:
sage: Sym = SymmetricFunctions(QQ) sage: p = Sym.p() sage: p.bottom_schur_function([2,2,1]) -1/6*p[3, 2] + 1/4*p[4, 1] sage: p.bottom_schur_function([2,1]) -1/3*p[3] sage: p.bottom_schur_function([3]) 1/3*p[3] sage: p.bottom_schur_function([1,1,1]) 1/3*p[3] sage: p.bottom_schur_function(Partition([1,1,1])) 1/3*p[3] sage: p.bottom_schur_function([2,1], degree=1) -1/3*p[3] sage: p.bottom_schur_function([2,1], degree=2) 0 sage: p.bottom_schur_function([2,1], degree=3) 1/3*p[1, 1, 1] sage: p.bottom_schur_function([2,2,1], degree=3) 1/8*p[2, 2, 1] - 1/6*p[3, 1, 1]
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SymmetricFunctionAlgebra_power.
coproduct_on_generators
(i)¶ Return coproduct on generators for power sums \(p_i\) (for \(i > 0\)).
The elements \(p_i\) are primitive elements.
INPUT:
self
– the power sum basis of the symmetric functionsi
– a positive integer
OUTPUT:
- the result of the coproduct on the generator \(p(i)\)
EXAMPLES:
sage: Sym = SymmetricFunctions(QQ) sage: p = Sym.powersum() sage: p.coproduct_on_generators(2) p[] # p[2] + p[2] # p[]
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SymmetricFunctionAlgebra_power.
eval_at_permutation_roots_on_generators
(k, rho)¶ Evaluate \(p_k\) at eigenvalues of permutation matrix.
This function evaluates a symmetric function
p([k])
at the eigenvalues of a permutation matrix with cycle structure\rho
.This function evaluates a \(p_k\) at the roots of unity
\[\Xi_{\rho_1},\Xi_{\rho_2},\ldots,\Xi_{\rho_\ell}\]where
\[\Xi_{m} = 1,\zeta_m,\zeta_m^2,\ldots,\zeta_m^{m-1}\]and \(\zeta_m\) is an \(m\) root of unity. This is characterized by \(p_k[ A , B ] = p_k[A] + p_k[B]\) and \(p_k[ \Xi_m ] = 0\) unless \(m\) divides \(k\) and \(p_{rm}[\Xi_m]=m\).
INPUT:
k
– a non-negative integerrho
– a partition or a list of non-negative integers
OUTPUT:
- an element of the base ring
EXAMPLES:
sage: p = SymmetricFunctions(QQ).p() sage: p.eval_at_permutation_roots_on_generators(3, [6]) 0 sage: p.eval_at_permutation_roots_on_generators(3, [3]) 3 sage: p.eval_at_permutation_roots_on_generators(3, [1]) 1 sage: p.eval_at_permutation_roots_on_generators(3, [3,3]) 6 sage: p.eval_at_permutation_roots_on_generators(3, [1,1,1,1,1]) 5