<s>
GEMPACK	B-General_Concept
(	O
General	O
Equilibrium	O
Modelling	O
PACKage	O
)	O
is	O
a	O
modeling	B-Application
system	O
for	O
CGE	O
economic	O
models	O
,	O
used	O
at	O
the	O
Centre	O
of	O
Policy	O
Studies	O
(	O
CoPS	O
)	O
in	O
Melbourne	O
,	O
Australia	O
,	O
and	O
sold	O
to	O
other	O
CGE	O
modellers	O
.	O
</s>
<s>
Some	O
of	O
the	O
more	O
well-known	O
CGE	O
models	O
solved	O
using	O
GEMPACK	B-General_Concept
are	O
the	O
GTAP	O
model	O
of	O
world	O
trade	O
,	O
and	O
the	O
MONASH	O
,	O
MMRF	O
,	O
ORANI-G	O
and	O
TERM	O
models	O
used	O
at	O
CoPS	O
.	O
</s>
<s>
All	O
these	O
models	O
share	O
a	O
distinctive	O
feature	O
:	O
they	O
are	O
formulated	O
as	O
a	O
system	O
of	O
differential	O
equations	O
in	O
percentage	O
change	O
form	O
;	O
however	O
,	O
this	O
is	O
not	O
required	O
by	O
GEMPACK	B-General_Concept
.	O
</s>
<s>
GEMPACK	B-General_Concept
builds	O
on	O
this	O
feature	O
by	O
formulating	O
the	O
CGE	O
model	O
as	O
an	O
initial	O
value	O
problem	O
which	O
is	O
solved	O
using	O
standard	O
techniques	O
.	O
</s>
<s>
The	O
GEMPACK	B-General_Concept
user	O
specifies	O
her	O
model	O
by	O
constructing	O
a	O
text	O
file	O
listing	O
model	O
equations	O
and	O
variables	O
,	O
and	O
showing	O
how	O
variables	O
relate	O
to	O
value	O
flows	O
stored	O
on	O
an	O
initial	O
data	O
file	O
.	O
</s>
<s>
GEMPACK	B-General_Concept
translates	O
this	O
file	O
into	O
a	O
computer	O
program	O
which	O
solves	O
the	O
model	O
,	O
i.e.	O
,	O
computes	O
how	O
model	O
variables	O
might	O
change	O
in	O
response	O
to	O
an	O
external	O
shock	O
.	O
</s>
<s>
Then	O
it	O
is	O
solved	O
by	O
multistep	O
methods	O
such	O
as	O
the	B-Algorithm
Euler	I-Algorithm
method	I-Algorithm
,	O
midpoint	B-Algorithm
method	I-Algorithm
or	O
Gragg	O
's	O
modified	O
Midpoint	B-Algorithm
method	I-Algorithm
.	O
</s>
<s>
These	O
all	O
require	O
solution	O
of	O
a	O
large	O
system	O
of	O
linear	O
equations	O
;	O
accomplished	O
by	O
sparse	B-Algorithm
matrix	I-Algorithm
techniques	O
.	O
</s>
<s>
Richardson	B-Algorithm
extrapolation	I-Algorithm
is	O
used	O
to	O
improve	O
accuracy	O
.	O
</s>
<s>
Additionally	O
it	O
has	O
lent	O
itself	O
to	O
some	O
interesting	O
extensions	O
,	O
such	O
as	O
:	O
a	O
Gaussian	B-Algorithm
quadrature	I-Algorithm
method	O
of	O
estimating	O
confidence	O
intervals	O
for	O
model	O
results	O
from	O
known	O
distributions	O
of	O
shock	O
or	O
parameter	O
values	O
;	O
a	O
way	O
to	O
formulate	O
inequality	O
constraints	O
or	O
non-differentiable	O
equations	O
as	O
complementarities	O
;	O
and	O
a	O
technique	O
to	O
decompose	O
changes	O
in	O
model	O
variables	O
due	O
to	O
several	O
shocks	O
into	O
components	O
due	O
to	O
each	O
individual	O
shock	O
.	O
</s>
<s>
The	O
underlying	O
numerical	O
approach	O
is	O
complemented	O
by	O
several	O
GUI	B-Application
programs	O
that	O
:	O
ease	O
viewing	O
of	O
large	O
multidimensional	O
arrays	O
often	O
found	O
in	O
CGE	O
databases	O
;	O
manage	O
complex	O
(	O
e.g.	O
,	O
multi-period	O
)	O
simulations	O
;	O
and	O
allow	O
interactive	O
exploration	O
and	O
explanation	O
of	O
simulation	O
results	O
.	O
</s>
