Implementing Quotas in GTAP Using GEMPACK or How to Linearize an Inequality

Note added March 2002 The methods described in the paper below have been automated as part of Release 8.0 of GEMPACK. This new version of GEMPACK (which is being beta tested by several modellers now and will be officially released later in 2002) makes it very easy to implement quotas (including import/export quotas and tariff rate quotas). This means that many of the implementation details in the technical paper below are no longer required. If you need to implement quotas etc in GEMPACK, please consult Ken Pearson. 1996, September. This document describes how explicit import and export quotas can be implemented and solved in the GTAP CGE trade model. The techniques described here apply equally well to other general and partial equilibrium models implemented and solved using the GEMPACK software. They also generalise to procedures for handling other inequalities in models solved via GEMPACK (even though GEMPACK does not allow explicit inequalities in the algebraic representation of models). In this document we review some recent applications of GTAP in which explicit import and export quotas have been modelled, and discuss how important it was for these applications to have explicit treatment of quotas. Accompanying this document are various computer files containing the ingredients of examples that readers can carry out for themselves while reading this paper. These files can also be used as a starting point for those who wish to explicitly model quotas in their own models.