Eero Hyvönen

Interval Computations on the Spreadsheet

This paper reviews work on using interval arithmetic as the basis for next generation spreadsheet programs capable of dealing with rounding errors, imprecise data, and numerical constraints. A series of ever more versatile computational models for spreadsheets are presented beginning with classical interval arithmetic and ending with interval constraint satisfaction. In order to demonstrate the ideas, an actual implementation of each model as a class library is presented and its integration with a commercial spreadsheet program is explained.

Interval constraint spreadsheets for financial planning

Spreadsheets are difficult to use in applications, where only incomplete or inexact data (e.g. intervals) are available-a typical situation in financial planning. The author argues that this is due to two fundamental shortcomings of the computational paradigm underlying spreadsheets: firstly, the distinction between input and output cells has to be fixed before computations; and secondly, cells may have only exact values. As a result, spreadsheets support the user only with primitive iterative problem solving schemes based on trial-and-error methods. He presents a constraint based computational paradigm for next generation interval spreadsheets. The scheme makes it possible to exploit incomplete/inexact data (intervals) and it can support problem solving in a top-down fashion. Current spreadsheets constitute a special case of the more general interval constraint spreadsheets proposed. >Spreadsheets are difficult to use in applications, where only incomplete or inexact data (e.g. intervals) are available-a typical situation in financial planning. The author argues that this is due to two fundamental shortcomings of the computational paradigm underlying spreadsheets: firstly, the distinction between input and output cells has to be fixed before computations; and secondly, cells may have only exact values. As a result, spreadsheets support the user only with primitive iterative problem solving schemes based on trial-and-error methods. He presents a constraint based computational paradigm for next generation interval spreadsheets. The scheme makes it possible to exploit incomplete/inexact data (intervals) and it can support problem solving in a top-down fashion. Current spreadsheets constitute a special case of the more general interval constraint spreadsheets proposed.<<ETX>>

A New Basis for Spreadsheet Computing: Interval Solver for Microsoft Excel

There is a fundamental mismatch between the computational basis of spreadsheets and our knowledge of the real world. In spreadsheets, numeric data are represented as exact numbers and their mutual relations as functions, whose values (output) are computed from given argument values (input). However, in the real world, data are often inexact and uncertain in many ways, and the relationships, that is, constraints, between input and output are far more complicated. This article shows that interval constraint solving, an emerging AI-based technology, provides a more versatile and useful foundation for spreadsheets. The new computational basis is 100-percent downward compatible with the traditional spreadsheet paradigm. The idea has been successfully integrated with Microsoft excel as the add-in interval solver that seamlessly upgrades the arithmetic core of excel into interval constraint solving. The product has been downloaded by thousands of end users all over the world and has been used in various applications in business computing, engineering, education, and science. There is an intriguing chance for a major breakthrough of the AI technology on the spreadsheet platform: Tens of millions of excel users are making important decisions based on spreadsheet calculations.

Interval constraint satisfaction tool INC

Numerical design and planning problems can often be formulated conveniently as a set of equations constraining the values of related variables, i.e., as a numerical or more generally as an interval constraint satisfaction problem (ICSP). However, due to theoretical and practical problems, no tools for solving ICSPs properly in the general case have thus far been designed and implemented. The authors discuss both theoretical and practical problems of solving ICSPs, and present solution approaches taken in the new interval constraint satisfaction tool INC++. The tool can be applied, for example, as the basis for next generation interval constraint spreadsheets.

Interval Input and Output

More and more novice users are starting to use interval extensions to programming languages and interval-based applications. An important question then is: What is the most simple and natural form to input and output intervals? This paper points out conceptual and practical difficulties encountered when interfacing end-users with intervals. A new interval formatting scheme is then proposed. It has been implemented in a commercial interval extension to Microsoft Excel spreadsheet program targeted to non-expert users.