tailieunhanh - Báo cáo toán học: "The number of elements in the mutation class of a quiver of type Dn Aslak Bakke Buan"

Tuyển tập các báo cáo nghiên cứu khoa học về toán học trên tạp chí toán học quốc tế đề tài: The number of elements in the mutation class of a quiver of type Dn Aslak Bakke Buan. | The number of elements in the mutation class of a quiver of type Dn Aslak Bakke Buan Department of Mathematical Sciences Norwegian University of Science and Technology Norway aslakb@ Hermund Andre Torkildsen Department of Mathematical Sciences Norwegian University of Science and Technology Norway hermunda@ Submitted Jan 20 2009 Accepted Apr 14 2009 Published Apr 22 2009 Mathematics Subject Classification 16G20 16G70 05E15 20F55 Abstract We show that the number of quivers in the mutation class of a quiver of Dynkin type Dn is given by d n d n d 2 2n for n 5. To obtain this formula we give a correspondence between the quivers in the mutation class and certain rooted trees. Introduction Quiver mutation is an important ingredient in the definition of cluster algebras FZ1 . It is an operation on quivers which induces an equivalence relation on the set of quivers. The mutation class M of a quiver Q consists of all quivers mutation equivalent to Q. If Q is a Dynkin quiver then M is finite. In T an excplicit formula for M is given for Dynkin type An. Here we give an explicit formula for the number of quivers in the mutation class of a quiver of Dynkin type Dn. The formula is given by d n Ed n 9 n d 2n if n 5. t 6 if n 4. where Ộ is the Euler function. The proof for this formula consists of two parts. The first part shows that the mutation class of type Dn is in 1-1 correspondence with the triangulations with tagged edges of THE ELECTRONIC JOURNAL OF COMBINATORICS 16 2009 R49 1 a punctured n-gon up to rotation and inversion of tags. This is a generalization of the method used in T to count the number of elements in the mutation class of quivers of Dynkin type An. Here we are strongly using the ideas in FST and S . In the second part we count the number of equivalence classes of triangulations of a punctured n-gon by describing an explicit correspondence to a certain class of rooted trees. A tree in this class is constructed by taking a family of full

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