International Dynamic Input-Output Modelling Language
IDIOM
The principal current author of IDIOM is Terry Barker; earlier authors are given in the references below. IDIOM is a FORTRAN90 program designed for the specification and solution of large-scale econometric non-linear simulation models incorporating a wide range of relationships, including input-output systems. IDIOM was originally written by the Cambridge Growth Project, Department of Applied Economics, University of Cambridge, the original package being funded by UNIDO to help provide software tools for industrial development. Since 1987, the use and development of IDIOM was taken over by Cambridge Econometrics Ltd, following the closure of the project in that year. IDIOM has been revised and extended by Cambridge Econometrics as the software platform for a number of econometric models covering economic, energy and environmental models for countries and regions, namely, the UK models MDM-E3 and LEFM, the Europe regional E3 model E3ME, and the global model E3MG. In 1989, IDIOM was re-written for compilation and solution using the Salford FORTRAN compiler FTN77 and the operating system DBOS, so that it could run models unconstrained by the 640k limitations of the IBM-PC-compatible 386 and 486 PCs. In 1997 the software was further developed so that it could be used as part of a user-friendly system for solving models under Windows 95. The latest version uses the Intel Fortran compiler.
The purpose of IDIOM is to provide a means of organising the historical data, the assumptions and the relationships of large econometric models, including those for inter-relating economies and regions of one economy, then solving the models over a number of periods and finally storing and presenting the results.
Various features of IDIOM are common across the models built and solved using the package (the housekeeping routines) and are described in the model manual. Other features have to be provided by the model builder as specific to the model. Builders of models should prepare a separate manual for model users; and users of the models should consult the appropriate model manual for details of a particular model.
IDIOM differs from other economic modelling solving packages, such as MODLER, AREMOS, EViews, or TROLL in two respects. Firstly the organising concept and principle of IDIOM is that of matrix algebra. In this it is more like the GAUSS or Ox packages than MODLER and others. The specification of equations can be in terms of industries or regions or both, so that one line of commands can replace many lines required by a package organised around scalar variables and equations for each such variable. This is particularly useful for cross-section, time-series econometric modelling involving large datasets. Secondly, IDIOM does not provide facilities for estimating equations or managing associated databanks. These tasks must be done using the MREG software package or the Ox programes developed by Cambridge Econometrics.
The main benefits from such specialisation are time-saving in computer calculations and ease of managing large models by organising solutions about matrix variables. IDIOM can solve and store large-scale E3 models (e.g. involving up to 20,000 estimated equations and over two million variables over a 30 year period) in little more than ten seconds on a modern PC. IDIOM operates by interpreting directives from the model-builder defining the specification of the model required and the computations to be performed. Since these directives are interpreted rather than compiled, substantial changes in the model structure can be made without knowledge of the internal program structure. In addition, the provision of facilities for the conditional or repeated execution of directives provides the model-builder with much of the control over the models normally obtained by writing in a conventional high-level computer language.
Terry Barker, William Peterson and Alan Winters (1984) 'An international dynamic input-output model', pp. 183-192 of UNIDO (ed.) Proceedings of the Seventh International Conference on Input-Output Techniques, United Nations, New York, 1984.
William Peterson (1987) 'Computer software for a large econometric model' in Terry Barker and William Peterson (eds.) The Cambridge Multisectoral Dynamic Model of the British Economy, Cambridge University Press, 1987
IDIOM User's Guide, Version 8 Release 1, October 2002.
For more information contact:
David Taylor
Company Administrator
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