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  • 1.
    Odeberg Hollifeldt, Samuel
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Matematisk-datavetenskapliga sektionen, Matematiska institutionen, Algebra, logik och representationsteori.
    Decomposing Certain Projectives in Category O2024Självständigt arbete på avancerad nivå (masterexamen), 20 poäng / 30 hpStudentuppsats (Examensarbete)
    Abstract [en]

    We introduce the BGG category O of a finite-dimensional semisimple Lie algebra g with the initial aims of providing a detailed introduction to the subject and establishing the main results of the original BGG paper [BGG76]. Our exposition mainly follows that of [Hum08] and [Maz20], with some refined and additional results. Once we have established the main results of [BGG76] we study three classes of modules that were used to show the existence of enough projectives in O. We find a description of their Verma flags and in the case of sl_2 we find their decompositions as direct sums of indecomposable projectives and for sl_3 we also do this for one of our module classes, which we can also use to show that composition factors of Verma modules occur only with multiplicity 1 or 0 for sl_3. After this we introduce translation functors and show that two blocks of O are equivalent under certain conditions and classify the projective-injectives of O, mainly following the exposition of [Hum08]. In the last section we introduce the Hecke algebra of a Coxeter system following [Hum90] and [Maz20]. Finally, we briefly touch on Kazhdan-Lusztig theory, culminating in a complete classification of which finite-dimensional semisimple Lie algebras g with Verma module multiplicities \geq 2 for regular integral weights.

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  • 2.
    Mustata, Anna
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Matematisk-datavetenskapliga sektionen, Matematiska institutionen, Algebra, logik och representationsteori.
    Multiparameter persistence and relative homological algebra2024Självständigt arbete på avancerad nivå (masterexamen), 20 poäng / 30 hpStudentuppsats (Examensarbete)
    Abstract [en]

    In topological data analysis we study a data set given as a finitepoint cloud by embedding it insome parameter-dependent topological spaces, and computing their homology. This can be formalised as thecomposition of two functors: first from a poset to the category of topological spaces, and then on to the category of vector spaces over a field. This is known as a filtration. Filtrations can be seen as modules over the path algebra of a quiver given by the Hasse diagram of the initial poset, or equivalently as quiver representations of this quiver. We obtain the ranks of morphisms in this quiver representation via relative projective resolutions for a suitably chosen exact structure. In order to show that this structure is exact we follow the proof of a theorem by Botnan, Opperman and Oudot, which we extend to work over all abelian categories rather than only categories of modules over Artin algebras. We conclude with a discussion of Auslander-Reiten theory in the context of exact categories.

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  • 3.
    Norlén Jäderberg, Mika
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Matematisk-datavetenskapliga sektionen, Matematiska institutionen, Algebra, logik och representationsteori.
    The Ext-Algebra of Standard Modules of Bound Twisted Double Incidence Algebras2023Självständigt arbete på avancerad nivå (masterexamen), 20 poäng / 30 hpStudentuppsats (Examensarbete)
    Abstract [en]

    Quasi-hereditary algebras are an important class of algebras with many appli-cations in representation theory, most notably the representation theory of semi-simple complex Lie-algebras. Such algebras sometimes admit an exact Borel sub-algebra, that is a subalgebra satisfying similar formal properties to the Borel sub-algebras from Lie theory. This thesis is divided into two parts. In the first part we classify quasi-hereditary algebras with two simple modules over perfect fields up to Morita equivalence, generalizing a similar result by Membrillo-Hernandez for thealgebraically closed case. In the second part, we take a poset X, a certain set M of constants, and a finite set ρ of paths in the Hasse-diagram of X and construct analgebra A(X, M, ρ) that generalizes the twisted double incidence algebras originally introduced by Deng and Xi. We provide necessary and sufficient conditions for this algebra to be quasi-hereditary when X is a tree, and we show that A(X, M, ρ) admits an exact Borel subalgebra when these conditions are satisfied. Following this, we compute the Ext-algebra of the standard modules of A(X, M, ρ).

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  • 4.
    Hildebrandsson, Victor
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Matematisk-datavetenskapliga sektionen, Matematiska institutionen.
    Octonion Algebras over Schemes and the Equivalence of Isotopes and Isometric Quadratic Forms2023Självständigt arbete på avancerad nivå (masterexamen), 20 poäng / 30 hpStudentuppsats (Examensarbete)
    Abstract [en]

    Octonion algebras are certain algebras with a multiplicative quadratic form. In 2019, Alsaody and Gille showed that, for octonion algebras over unital commutative rings, there is an equivalence between isotopes and isometric quadratic forms. The contravariant equivalence from unital commutative rings to affine schemes, sending a ring to its spectrum, leads us to a question: can the equivalence of isometry and isotopy be generalized to octonion algebras over a (not necessarily affine) scheme? We present the basic definitions and properties of octonion algebras, both over rings and over schemes. Then we show that an isotope of an octonion algebra C over a scheme is isomorphic to a twist by an Aut(C)–torsor. We conclude the thesis by giving an affirmative answer to our question.

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  • 5.
    Lindell, Jonathan
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Matematisk-datavetenskapliga sektionen, Matematiska institutionen, Algebra, logik och representationsteori.
    Relative Hochschild (co)homology2022Självständigt arbete på avancerad nivå (masterexamen), 20 poäng / 30 hpStudentuppsats (Examensarbete)
    Abstract [en]

    We study relative homological algebra and relative Hochschild cohomology. We dualise the construction in [Cib+21b] for a ring extension B ⊆ A to construct a long nearly exact sequence for the relative Hochschild cohomology HH∗(A|B), the Hochschild cohomology HH∗(A) and the Hochschild cohomology HH∗(B,A). Parallel to this we also study corings and the associated Cartier cohomology and Hochschild cohomology. Given an A-coring C and its right algebra R we have induced maps ExtiA(M, N) → ExtiR(R⊗A M, R⊗A N) by the induction functor. We characterise the vanishing of the Hochschild cohomology of the coring in terms of these induced maps being isomorphisms for degrees greater than or equal to one.

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  • 6.
    Ali, Hassan
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Matematisk-datavetenskapliga sektionen, Matematiska institutionen, Algebra, logik och representationsteori.
    Exceptional Groups and their Generators2022Självständigt arbete på avancerad nivå (masterexamen), 20 poäng / 30 hpStudentuppsats (Examensarbete)
    Abstract [en]

    Exceptional algebraic groups are divided into five types, namely G2, F4,E6, E7 and E8. In this thesis we discuss G2, F4 and E6. We discuss the exceptionalalgebraic groups via octonion algebras and Jordan algebras. We firstconsider the groups of type G2. Groups of type G2 are automorphism groupsof octonion algebras, a form of composition algebras. We take the algebra of Zorn vector matrices and find the possible values of automorphisms of thisalgebra with the help of U-operators. We also discuss the product of two andthree U-operators. Then we discuss Albert algebras, since groups of type E6and F4 are related to these algebras. The Albert algebras are a form of Jordanalgebras. We also study the U-operators in Albert algebras. In this thesis wework over algebraically closed fields of characteristic zero.

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  • 7.
    Waara, Einar
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Matematisk-datavetenskapliga sektionen, Matematiska institutionen, Algebra, logik och representationsteori.
    The Weak Lefschetz Property For Artinian Quadratic Monomial Algebras2022Självständigt arbete på avancerad nivå (masterexamen), 20 poäng / 30 hpStudentuppsats (Examensarbete)
    Abstract [en]

    In this thesis we aim to study the Lefschetz properties ofmonomial algebras. First, we present the necessary concepts and resultsfrom commutative algebra, in particular we build up to the Hilbert-Serre theorem regarding the rationality of Hilbert series. We then reviewsome important results from the literature on the Lefschetz properties(whereof many provide drastic computational shortcuts under certainconditions) and provide some examples of these. The second half isdevoted to the study of Artinian quadratic monomial algebras of theform A(Δ) = K[x1, . . . , xn]/JΔ, where JΔ = (x21, . . . , x2n) + IΔ and IΔis the ideal obtained from some (abstract) simplicial complex Δ viathe Stanley-Reisner correspondence. In particular, we review a recentarticle [2] by H. Dao and R. Nair, provide examples and refine some ofthe formulations and results.

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  • 8.
    Tsang, Hin Chung Henry
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Matematisk-datavetenskapliga sektionen, Matematiska institutionen, Algebra, logik och representationsteori.
    Higher preprojective algebras and higherAuslander algebras2022Självständigt arbete på avancerad nivå (masterexamen), 20 poäng / 30 hpStudentuppsats (Examensarbete)
    Abstract [en]

    Let Q be a Dynkin quiver of type A and K be an algebraically closedfield. We start with the preprojective algebra Λ associated to Q andpresent a 2-cluster tilting module of Λ constructed by Geiss, Leclerc, andSchr¨oer.After that we move on to something more general. Let A be a drepresentationfinite algebra, its (d+1)-preprojective algebra has a (d+1)-cluster tilting module given by Iyama and Opperman, we shall comparethis with the case d = 1. Then we will compute an example where d = 2. In both cases we will investigate the endomorphism algebra of thecorresponding d-cluster tilting module.

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  • 9.
    Cuszynski-Kruk, Mikolaj
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Matematisk-datavetenskapliga sektionen, Matematiska institutionen, Algebra, logik och representationsteori.
    Perron–Frobenius theorem and Z≥0[S3]-semimodules2022Självständigt arbete på avancerad nivå (masterexamen), 20 poäng / 30 hpStudentuppsats (Examensarbete)
    Abstract [en]

    In this thesis, the Perron–Frobenius theorem which in its most general formstates that the spectral radius of a non-negative real square matrix is an eigenvaluewith a non-negative eigenvector, is proven. Related properties arederived, in particular the Collatz–Wielandt formula and a general form of anon-negative idempotent matrices. Furthermore, let Rn be the sub-semi-ringof Z≥0[Sn] generated by the Kazhdan–Lusztig basis. a description of R2-semimodules,R3-semi-modules and a classification of elementary R3-semi-modulesis given.

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  • 10.
    Gustavsson, Bim
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Matematisk-datavetenskapliga sektionen, Matematiska institutionen, Algebra, logik och representationsteori.
    Classification Of Finite-Dimensional Complex Semi-Simple Lie Algebras And Serre’s Theorem2022Självständigt arbete på avancerad nivå (masterexamen), 20 poäng / 30 hpStudentuppsats (Examensarbete)
    Abstract [en]

    We consider finite-dimensional complex semi-simple Lie algebras g. Any such Lie algebra has a Cartan subalgebra h, and its adjoint representation on g yields a root space decomposition of g, which in turn gives rise to a root system. These are in turn classified by the Dynkin diagrams. Conversely, for any root system, there is a corresponding semi-simple Lie algebra, and the complex semi-simple Lie algebras are therefore classified by the root system. Given a root system, Serre’s theorem states explicitly how to reconstruct corresponding semi-simple Lie algebra from this root system.

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  • 11.
    Matsson, Isak
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Matematisk-datavetenskapliga sektionen, Matematiska institutionen, Algebra och geometri.
    Algebras in Monoidal Categories2021Självständigt arbete på avancerad nivå (masterexamen), 20 poäng / 30 hpStudentuppsats (Examensarbete)
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  • 12.
    Wang, Ruoyu
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Matematisk-datavetenskapliga sektionen, Matematiska institutionen, Algebra och geometri.
    Symmetric Functions and Kronecker Coefficients2021Självständigt arbete på avancerad nivå (masterexamen), 20 poäng / 30 hpStudentuppsats (Examensarbete)
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  • 13.
    Berg, Sandra
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Matematisk-datavetenskapliga sektionen, Matematiska institutionen, Algebra och geometri.
    Global dimension of (higher) Nakayama algebras2020Självständigt arbete på avancerad nivå (masterexamen), 20 poäng / 30 hpStudentuppsats (Examensarbete)
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  • 14.
    Pérez Manríquez, Alejandra
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Matematisk-datavetenskapliga sektionen, Matematiska institutionen, Algebra och geometri.
    Quivers for semigroup algebras of binary relations of small rank2020Självständigt arbete på avancerad nivå (masterexamen), 20 poäng / 30 hpStudentuppsats (Examensarbete)
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  • 15.
    Stroiński, Mateusz
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Matematisk-datavetenskapliga sektionen, Matematiska institutionen, Algebra och geometri.
    Simple Transitive 2-Representations of Cell 2-Subcategories for Algebras with a Self-Injective Core2020Självständigt arbete på avancerad nivå (masterexamen), 20 poäng / 30 hpStudentuppsats (Examensarbete)