The Hessenberg Indexing Function
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.
A ≔ Array⁡Hessenbergupper,1..4,1..4,a,b→a+b
M ≔ Matrix⁡3,1,1,1,1,1,1,1,1,1,shape=Hessenberglower
M1,2 ≔ 5
M1,3 ≔ 5
Error, attempt to assign to upper triangle of lower Hessenberg rtable
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