The Hessenberg indexing function can be used to construct rtable objects of type Array or Matrix.

In the construction of a Matrix, if Hessenberg or Hessenberg[upper] is included in the calling sequence as an indexing function (shape), an upper Hessenberg Matrix is returned.

Note:  A Hessenberg Matrix is a triangular Matrix with one extra (contiguous) diagonal.

This indexing function may also be qualified as Hessenberg[lower].

The specification is similar in the construction of an Array.

If an object is defined by using the Hessenberg or Hessenberg[upper] indexing function, the elements located in the lower triangle, below the subdiagonal, cannot be reassigned.

The situation is similar in a construction that uses Hessenberg[lower] as an indexing function.

Error, attempt to assign to upper triangle of lower Hessenberg rtable