New Features in Release 5.2 of GEMPACK

This describes features of Release 5.2 (September 1996) of GEMPACK which were not available in Release 5.1 (April 1994) of GEMPACK. These include:

• TABLO-like statements in Command files to display values or to define new sets without having to rerun TABLO
• Set and element labelling on Header Array files makes output from SEEHAR etc easier to read
• WinGEM, a Windows interface to GEMPACK on Windows and Windows 95 PCs, allows modellers to work in the familiar Windows environment instead of the old DOS prompt
• New sparse-matrix software solves many models (especially multi-regional and intertemporal ones) more quickly
• Users can specify the accuracy they require when carrying out simulations instead of having to guess in advance how many steps are required
• Procedures have been developed and automated recently
  1. for doing systematic sensitivity analysis, and
  2. for handling inequalities including modelling of explicit import and export volume quotas
• Several new statements in TABLO Input files allow more direct specification of sets and conditions, explicit mappings between sets and checks of data

Some details are given below.

TABLO-like statements in Command files

When running GEMSIM or TABLO-generated programs, extra TABLO-like statements (for example, declaring extra sets or asking for extra WRITEs or DISPLAYs) can be included in the Command file. Such statements are carried out as if they were appended to the end of the original TABLO Input file.

Set and element labelling on Header Array files

Arrays on Header Array files can now contain set and element labelling information, namely the names of the coefficients usually associated with the arrays, the names of the sets over which the arguments of the array run and the names of the elements of the sets involved with the array. TABLO-generated programs and GEMSIM now automatically write this information to any arrays they write to a Header Array file. This information is shown in SEEHAR output and also when SLTOHT produces Header Array output (the default) or when the new option 'SSE' is selected. It is also shown by VIEWHAR (see below).

WinGEM - Windows interface

When GEMPACK runs on DOS machines under Microsoft Windows or Windows95, it can be run under a new GEMPACK Windows interface called WinGEM. Users can carry out modelling tasks using GEMPACK windows. We hope that this will make modelling easier for both new and experienced modellers using these machines. As part of this, a new Windows program VIEWHAR (written by our colleague Mark Horridge) allows windows-type access to examine the data in Header Array files. [You can think of VIEWHAR as a Windows version of SEEHAR.]

Solving models

New sparse linear equation solving routines MA48 (sometimes a faster alternative to the MA28 routines) are now the default. The new routines are usually significantly faster for multi-regional models (including GTAP) and intertemporal models, though they are not faster for some single-country models (for example, MONASH).

User-specified accuracy

You can now specify in advance what accuracy you require for simulations carried out via TABLO-generated programs or GEMSIM. You specify what accuracy you require (how many significant figures) and what percentage of results you require to be this accurate and the program works out how many steps and how many subintervals are required to achieve this accuracy.

Improved TABLO syntax

• SET complement syntax, for example
  SET NONMARCOM = COM - MARCOM ;
  is allowed in TABLO Input files.
• Sets can be defined in TABLO Input files in ways which depend on data, as in for example,
  SET SPCOM = (all,c,COM: TOTX(c) > TOTY(c)/5 ) ;
  which says that the set SPCOM consists of all commodities c in COM for which TOTX(c) is greater than one-fifth of TOTY(c).
• Explicit mappings between sets (for example, a mapping from unique-product industries to unique-product commodities, mapping each industry to the commodity it makes) are available in TABLO Input files.
• A new function $POS is allowed which can be used to indicate the position number of an index or element in a set in TABLO Input files.
• A new type of statement called ASSERTION is allowed in TABLO Input files. These allow modellers to request that conditions they expect to hold be checked. For example, the following ASSERTION statement requests the software to check that no entries in a certain array are negative.

  ASSERTION # Check no negative values # 
                    (all,c,COM) DVHOUS(c) >= 0 ;
  

• New conditionals involving indices and/or set mappings explicitly, for example "IF( i EQ j, expression )", are available in TABLO Input files.
• It is now possible to write updated (that is, post-simulation) values of coefficients initialised via a FORMULA(INITIAL).

Other new features

• Newton's method for solving levels equations is now available. TABLO is used to add the appropriate Newton correction term to levels equations. When running a simulation using GEMSIM or the TABLO-generated program, the shock to the Newton variable can be added to the usual shocks in an Euler solution, or the Newton shock can be applied alone in a series of Newton correction steps applied after the original Euler multi-step simulation.
• A facility for translating GEMPACK Header Array files to GAMS format. [There is also a complementary facility available in GAMS for translating GAMS data files to GEMPACK format.]