Title: Adding Accounting-Related Behaviour to a Model Implemented Using GEMPACK

Authors: W.J. Harrison and K.R. Pearson

Abstract

Many modellers need to add new behaviour to an existing model which is implemented
using GEMPACK. In many such cases, the new behaviour is intimately connected with the
accounting relations in the model. An example is the task of adding new taxes to a model.
The aim of this paper is to give some guidance to modellers faced with such model
extensions.

Most models implemented in GEMPACK are written down as systems of linearised
equations. Others are written as systems of mixed levels/linearised equations or of just
levels equations. Adding accounting-related behaviour to linearised TABLO Input files is
probably less straight forward than adding it to mixed or completely levels files.

Irrespective of the style of the equations in the original TABLO Input file, the first
task is to write down the levels equations describing the new behaviour.

New data may be required, and care must also be taken with this. In particular, the
new data must be set up so that the new levels equations of the model are satisfied in
the pre-simulation data base (as well as the equations of the existing model).

In the paper a relatively simple example of accounting-related behaviour is
considered, namely adding a form of consumption tax to the Stylized Johansen model. The
paper describes how this behaviour can be added to the standard linearised TABLO Input
file SJLN.TAB for Stylized Johansen. In particular the paper shows how the new behaviour
can be added as linearised equations or as levels equations.