Modelling & training > Our suite of models > International Dynamic Input-Output Modelling Language
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:
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.
IDIOM is more specialised than the majority of other software packages for solving economic models, principally because it is not the intention to allow the user to build a model using the IDIOM modelling language alone and then 'run IDIOM' to solve the model, in the same way one might build and solve a model in MODLER, AREMOS, EViews, TROLL or GAMS. Instead, IDIOM provides a library of routines for data handling, parsing and solution for the user to include, allowing the user to concentrate on coding the economic logic of their model. The compiled model can then be run with sets of instructions written in the IDIOM modelling language to flexibly and easily change the input data, parameters and assumptions in solution without having to expose the less-technical user to the potentially very complicated underlying code. A further benefit is that actual computation takes place using compiled, rather than interpreted code (as might be found in another software package that offers facilities to specify equations in algebraic form); solution time is reduced as a consequence.
The key data unit in IDIOM is the matrix (which may be disaggregated by, for example, industries and/or regions) and the modelling language provides facilities to perform read/write and mathematical operations both element-by-element as well as on entire matrices. For large-scale economic modelling involving large datasets, this approach is more efficient than a package organised around scalar variables and equations for each such variable: a single line in IDIOM replaces many lines in a scalar-based package.
IDIOM also does not provide facilities for estimating equations or managing associated databanks. These tasks must be done separately, for example using the Ox programs developed by Cambridge Econometrics.
IDIOM is thus a package to provide facilities for organising, controlling and solving a model, rather than a system for building and estimating one by itself.
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 6, July 2007.
For more information contact:
Hector Pollitt
Associate Director, International Modelling