909 research outputs found

    Lattice Diagram Polynomials and Extended Pieri Rules

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    The lattice cell in the i+1st{i+1}^{st} row and j+1st{j+1}^{st} column of the positive quadrant of the plane is denoted (i,j)(i,j). If μ\mu is a partition of n+1n+1, we denote by μ/ij\mu/ij the diagram obtained by removing the cell (i,j)(i,j) from the (French) Ferrers diagram of μ\mu. We set Δμ/ij=detxipjyiqji,j=1n\Delta_{\mu/ij}=\det \| x_i^{p_j}y_i^{q_j} \|_{i,j=1}^n, where (p1,q1),...,(pn,qn)(p_1,q_1),... ,(p_n,q_n) are the cells of μ/ij\mu/ij, and let Mμ/ij{\bf M}_{\mu/ij} be the linear span of the partial derivatives of Δμ/ij\Delta_{\mu/ij}. The bihomogeneity of Δμ/ij\Delta_{\mu/ij} and its alternating nature under the diagonal action of SnS_n gives Mμ/ij{\bf M}_{\mu/ij} the structure of a bigraded SnS_n-module. We conjecture that Mμ/ij{\bf M}_{\mu/ij} is always a direct sum of kk left regular representations of SnS_n, where kk is the number of cells that are weakly north and east of (i,j)(i,j) in μ\mu. We also make a number of conjectures describing the precise nature of the bivariate Frobenius characteristic of Mμ/ij{\bf M}_{\mu/ij} in terms of the theory of Macdonald polynomials. On the validity of these conjectures, we derive a number of surprising identities. In particular, we obtain a representation theoretical interpretation of the coefficients appearing in some Macdonald Pieri Rules.Comment: 77 pages, Te

    Orthonormal Systems in Linear Spans

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    We show that any NN-dimensional linear subspace of L2(T)L^2(\mathbb{T}) admits an orthonormal system such that the L2L^2 norm of the square variation operator V2V^2 is as small as possible. When applied to the span of the trigonometric system, we obtain an orthonormal system of trigonometric polynomials with a V2V^2 operator that is considerably smaller than the associated operator for the trigonometric system itself.Comment: 18 page

    Parallelogram polyominoes, the sandpile model on a complete bipartite graph, and a q,t-Narayana polynomial

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    We classify recurrent configurations of the sandpile model on the complete bipartite graph K_{m,n} in which one designated vertex is a sink. We present a bijection from these recurrent configurations to decorated parallelogram polyominoes whose bounding box is a m*n rectangle. Several special types of recurrent configurations and their properties via this bijection are examined. For example, recurrent configurations whose sum of heights is minimal are shown to correspond to polyominoes of least area. Two other classes of recurrent configurations are shown to be related to bicomposition matrices, a matrix analogue of set partitions, and (2+2)-free partially ordered sets. A canonical toppling process for recurrent configurations gives rise to a path within the associated parallelogram polyominoes. This path bounces off the external edges of the polyomino, and is reminiscent of Haglund's well-known bounce statistic for Dyck paths. We define a collection of polynomials that we call q,t-Narayana polynomials, defined to be the generating function of the bistatistic (area,parabounce) on the set of parallelogram polyominoes, akin to the (area,hagbounce) bistatistic defined on Dyck paths in Haglund (2003). In doing so, we have extended a bistatistic of Egge, Haglund, Kremer and Killpatrick (2003) to the set of parallelogram polyominoes. This is one answer to their question concerning extensions to other combinatorial objects. We conjecture the q,t-Narayana polynomials to be symmetric and prove this conjecture for numerous special cases. We also show a relationship between Haglund's (area,hagbounce) statistic on Dyck paths, and our bistatistic (area,parabounce) on a sub-collection of those parallelogram polyominoes living in a (n+1)*n rectangle

    Combinatorics of Labelled Parallelogram polyominoes

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    We obtain explicit formulas for the enumeration of labelled parallelogram polyominoes. These are the polyominoes that are bounded, above and below, by north-east lattice paths going from the origin to a point (k,n). The numbers from 1 and n (the labels) are bijectively attached to the nn north steps of the above-bounding path, with the condition that they appear in increasing values along consecutive north steps. We calculate the Frobenius characteristic of the action of the symmetric group S_n on these labels. All these enumeration results are refined to take into account the area of these polyominoes. We make a connection between our enumeration results and the theory of operators for which the intergral Macdonald polynomials are joint eigenfunctions. We also explain how these same polyominoes can be used to explicitly construct a linear basis of a ring of SL_2-invariants.Comment: 25 pages, 9 figure

    Lattice Diagram polynomials in one set of variables

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    The space Mμ/i,jM_{\mu/i,j} spanned by all partial derivatives of the lattice polynomial Δμ/i,j(X;Y)\Delta_{\mu/i,j}(X;Y) is investigated in math.CO/9809126 and many conjectures are given. Here, we prove all these conjectures for the YY-free component Mμ/i,j0M_{\mu/i,j}^0 of Mμ/i,jM_{\mu/i,j}. In particular, we give an explicit bases for Mμ/i,j0M_{\mu/i,j}^0 which allow us to prove directly the central {\sl four term recurrence} for these spaces.Comment: 15 page
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