A generating function that counts the combinatorial full-span sub array structure of a regular array with some applications to APL

  • Authors:
  • Ronald I. Frank

  • Affiliations:
  • Pace University, Pleasantville, NY

  • Venue:
  • Proceedings of the 2003 conference on APL: stretching the mind
  • Year:
  • 2003

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Abstract

Using a radically new way of representing arrays, we present a formalism that expands (or decomposes) a regular array into a weighted sum of null arrays. We show that this "polynomial" expansion (1.16) exhaustively represents the regular full-span array sub structure of the original array. Full-span means full length in the dimensions used. The polynomial is a generating function whose coefficients of which count and indicate the shape of the regular full-span sub arrays of the given regular array. These results are all structural. They do not use knowledge of the particular data contents of the arrays. We apply this new decomposition to catenation and lamination and uncover some new insights into array structure.The decomposition and the algebraic results provide a unifying view and new formalism for regular multi-dimensional arrays. It has application wherever multi-dimensional arrays are used, particularly to generalized hyper cube architectures, OLAP hierarchical data structures, and array oriented languages. It subsumes some previous results. Some of these applications are indicated with their bibliography.There is a combinatorial argument on the shape vector that could generate the coefficients, but it does not give the structural insight of this approach.