Koszul algebra

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In abstract algebra, a Koszul algebra $R$ is a graded $k$ -algebra over which the ground field $k$ has a linear minimal graded free resolution, i.e., there exists an exact sequence:

$\cdots \rightarrow R(-i)^{{b_{i}}}\rightarrow \cdots \rightarrow R(-2)^{{b_{2}}}\rightarrow R(-1)^{{b_{1}}}\rightarrow R\rightarrow k\rightarrow 0.$

It is named after the French mathematician Jean-Louis Koszul.

We can choose bases for the free modules in the resolution; then the maps can be written as matrices. For a Koszul algebra, the entries in the matrices are zero or linear forms.

An example of a Koszul algebra is a polynomial ring over a field, for which the Koszul complex is the minimal graded free resolution of the ground field. There are Koszul algebras whose ground fields have infinite minimal graded free resolutions, e.g, $R=k[x,y]/(xy)$

References

R. Froberg, Koszul Algebras, In: Advances in Commutative Ring Theory. Proceedings of the 3rd International Conference, Fez, Lect. Notes Pure Appl. Math. 205, Marcel Dekker, New York, 1999, pp. 337–350.
J.-L. Loday, B. Vallette Algebraic Operads, Springer, 2012.
A. Beilinson, V. Ginzburg, W. Soergel, "Koszul duality patterns in representation theory", J. Amer. Math. Soc. 9 (1996) 473–527.
V. Mazorchuk, S. Ovsienko, C. Stroppel, "Quadratic duals, Koszul dual functors, and applications", Trans. of the AMS 361 (2009) 1129-1172.

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