• Title/Summary/Keyword: unstable algebra

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ON PETERSON'S OPEN PROBLEM AND REPRESENTATIONS OF THE GENERAL LINEAR GROUPS

  • Phuc, Dang Vo
    • Journal of the Korean Mathematical Society
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    • v.58 no.3
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    • pp.643-702
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    • 2021
  • Fix ℤ/2 is the prime field of two elements and write 𝒜2 for the mod 2 Steenrod algebra. Denote by GLd := GL(d, ℤ/2) the general linear group of rank d over ℤ/2 and by ${\mathfrak{P}}_d$ the polynomial algebra ℤ/2[x1, x2, …, xd] as a connected unstable 𝒜2-module on d generators of degree one. We study the Peterson "hit problem" of finding the minimal set of 𝒜2-generators for ${\mathfrak{P}}_d$. Equivalently, we need to determine a basis for the ℤ/2-vector space $$Q{\mathfrak{P}}_d:={\mathbb{Z}}/2{\otimes}_{\mathcal{A}_2}\;{\mathfrak{P}}_d{\sim_=}{\mathfrak{P}}_d/{\mathcal{A}}^+_2{\mathfrak{P}}_d$$ in each degree n ≥ 1. Note that this space is a representation of GLd over ℤ/2. The problem for d = 5 is not yet completely solved, and unknown in general. In this work, we give an explicit solution to the hit problem of five variables in the generic degree n = r(2t - 1) + 2ts with r = d = 5, s = 8 and t an arbitrary non-negative integer. An application of this study to the cases t = 0 and t = 1 shows that the Singer algebraic transfer of rank 5 is an isomorphism in the bidegrees (5, 5 + (13.20 - 5)) and (5, 5 + (13.21 - 5)). Moreover, the result when t ≥ 2 was also discussed. Here, the Singer transfer of rank d is a ℤ/2-algebra homomorphism from GLd-coinvariants of certain subspaces of $Q{\mathfrak{P}}_d$ to the cohomology groups of the Steenrod algebra, $Ext^{d,d+*}_{\mathcal{A}_2}$ (ℤ/2, ℤ/2). It is one of the useful tools for studying these mysterious Ext groups.

INVARIANT RINGS AND DUAL REPRESENTATIONS OF DIHEDRAL GROUPS

  • Ishiguro, Kenshi
    • Journal of the Korean Mathematical Society
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    • v.47 no.2
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    • pp.299-309
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    • 2010
  • The Weyl group of a compact connected Lie group is a reflection group. If such Lie groups are locally isomorphic, the representations of the Weyl groups are rationally equivalent. They need not however be equivalent as integral representations. Turning to the invariant theory, the rational cohomology of a classifying space is a ring of invariants, which is a polynomial ring. In the modular case, we will ask if rings of invariants are polynomial algebras, and if each of them can be realized as the mod p cohomology of a space, particularly for dihedral groups.

A study on the pre-multiplier model for redundant manipulator (여유자유도를 가진 로보트의 pre-multiplier모델에 관한 연구)

  • ;;P. Chosla
    • 제어로봇시스템학회:학술대회논문집
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    • 1989.10a
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    • pp.127-130
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    • 1989
  • The redundant manipulator extends the application fields of classical nonredundant manipulators. In this paper, we propose Premultiplier Model that describes the static behavior of redundant manipulator. This model provides insight and intuition about algebra and physics related to redundant manipulators. Active operational space stiffness control of redundant manipulators is proved to be always unstable and we propose a technique, based on our methodology, to make stiffness control stable.

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INVARIANT RINGS AND REPRESENTATIONS OF SYMMETRIC GROUPS

  • Kudo, Shotaro
    • Bulletin of the Korean Mathematical Society
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    • v.50 no.4
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    • pp.1193-1200
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    • 2013
  • The center of the Lie group $SU(n)$ is isomorphic to $\mathbb{Z}_n$. If $d$ divides $n$, the quotient $SU(n)/\mathbb{Z}_d$ is also a Lie group. Such groups are locally isomorphic, and their Weyl groups $W(SU(n)/\mathbb{Z}_d)$ are the symmetric group ${\sum}_n$. However, the integral representations of the Weyl groups are not equivalent. Under the mod $p$ reductions, we consider the structure of invariant rings $H^*(BT^{n-1};\mathbb{F}_p)^W$ for $W=W(SU(n)/\mathbb{Z}_d)$. Particularly, we ask if each of them is a polynomial ring. Our results show some polynomial and non-polynomial cases.

MODULAR INVARIANTS UNDER THE ACTIONS OF SOME REFLECTION GROUPS RELATED TO WEYL GROUPS

  • Ishiguro, Kenshi;Koba, Takahiro;Miyauchi, Toshiyuki;Takigawa, Erika
    • Bulletin of the Korean Mathematical Society
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    • v.57 no.1
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    • pp.207-218
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    • 2020
  • Some modular representations of reflection groups related to Weyl groups are considered. The rational cohomology of the classifying space of a compact connected Lie group G with a maximal torus T is expressed as the ring of invariants, H*(BG; ℚ) ≅ H*(BT; ℚ)W(G), which is a polynomial ring. If such Lie groups are locally isomorphic, the rational representations of their Weyl groups are equivalent. However, the integral representations need not be equivalent. Under the mod p reductions, we consider the structure of the rings, particularly for the Weyl group of symplectic groups Sp(n) and for the alternating groups An as the subgroup of W(SU(n)). We will ask if such rings of invariants are polynomial rings, and if each of them can be realized as the mod p cohomology of a space. For n = 3, 4, the rings under a conjugate of W(Sp(n)) are shown to be polynomial, and for n = 6, 8, they are non-polynomial. The structures of H*(BTn-1; 𝔽p)An will be also discussed for n = 3, 4.