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.