A hollow matrix is one with zero diagonal elements (according to this web page)
Q1: Is there a name for an upper (or lower) triangular hollow matrix?
Q2: Alternatively how might such an object be written using conventional notation?
I took a look at this web page, and the only objects which come close are the Hessenberg matrices, but clearly not close enough !
I suppose I could say "... upper triangular matrix with zero diagonal elements," or "... upper triangular hollow matrix," but a more succinct expression would be nice...