Counting symmetric nilpotent matrices

We determine the number of nilpotent matrices of order n over Fq that are self-adjoint for a given nondegenerate symmetric bilinear form, and in particular find the number of symmetric nilpotent matrices. Keywords: Nilpotent; symmetric; matrix; endomorphism; enumeratio

The probability that an operator is nilpotent

Choose a random linear operator on a vector space of finite cardinality N: then the probability that it is nilpotent is 1/N. This is a linear analogue of the fact that for a random self-map of a set of cardinality N, the probability that some iterate is constant is 1/N. The first result is due to Fine, Herstein and Hall, and the second is essentially Cayley's tree formula. We give a new proof of the result on nilpotents, analogous to Joyal's beautiful proof of Cayley's formula. It uses only general linear algebra and avoids calculation entirely.Comment: 5 pages, title change

Counting symmetric nilpotent matrices

We determine the number of nilpotent matrices of order n over Fq that are self-adjoint for a given nondegenerate symmetric bilinear form, and in particular find the number of symmetric nilpotent matrices. Keywords: Nilpotent; symmetric; matrix; endomorphism; enumeratio