<s>
GADGET	B-Application
is	O
free	B-Application
software	I-Application
for	O
cosmological	O
N-body/SPH	O
simulations	O
written	O
by	O
Volker	O
Springel	O
at	O
the	O
Max	O
Planck	O
Institute	O
for	O
Astrophysics	O
.	O
</s>
<s>
It	O
is	O
released	O
under	O
the	O
GNU	B-License
GPL	I-License
.	O
</s>
<s>
GADGET	B-Application
computes	O
gravitational	O
forces	O
with	O
a	O
hierarchical	O
tree	O
algorithm	O
(	O
optionally	O
in	O
combination	O
with	O
a	O
particle-mesh	O
scheme	O
for	O
long-range	O
gravitational	O
forces	O
)	O
and	O
represents	O
fluids	O
by	O
means	O
of	O
smoothed-particle	B-Application
hydrodynamics	I-Application
(	O
SPH	O
)	O
.	O
</s>
<s>
In	O
all	O
these	O
types	O
of	O
simulations	O
,	O
GADGET	B-Application
follows	O
the	O
evolution	O
of	O
a	O
self-gravitating	O
collisionless	O
N-body	B-Algorithm
system	O
,	O
and	O
allows	O
gas	O
dynamics	O
to	O
be	O
optionally	O
included	O
.	O
</s>
<s>
Both	O
the	O
force	O
computation	O
and	O
the	O
time	O
stepping	O
of	O
GADGET	B-Application
are	O
fully	O
adaptive	O
,	O
with	O
a	O
dynamic	O
range	O
which	O
is	O
,	O
in	O
principle	O
,	O
unlimited	O
.	O
</s>
<s>
GADGET	B-Application
can	O
therefore	O
be	O
used	O
to	O
address	O
a	O
wide	O
array	O
of	O
astrophysically	O
interesting	O
problems	O
,	O
ranging	O
from	O
colliding	O
and	O
merging	O
galaxies	O
,	O
to	O
the	O
formation	O
of	O
large-scale	O
structure	O
in	O
the	O
universe	O
.	O
</s>
<s>
With	O
the	O
inclusion	O
of	O
additional	O
physical	O
processes	O
such	O
as	O
radiative	O
cooling	O
and	O
heating	O
,	O
GADGET	B-Application
can	O
also	O
be	O
used	O
to	O
study	O
the	O
dynamics	O
of	O
the	O
gaseous	O
intergalactic	O
medium	O
,	O
or	O
to	O
address	O
star	O
formation	O
and	O
its	O
regulation	O
by	O
feedback	O
processes	O
.	O
</s>
<s>
The	O
first	O
public	O
version	O
(	O
GADGET-1	O
,	O
released	O
in	O
March	O
2000	O
was	O
created	O
as	O
part	O
of	O
Volker	O
's	O
PhD	O
project	O
under	O
the	O
supervision	O
of	O
Simon	O
White	O
.	O
</s>
<s>
The	O
second	O
public	O
version	O
(	O
GADGET-2	O
,	O
released	O
in	O
May	O
2005	O
contains	O
most	O
of	O
these	O
improvements	O
,	O
except	O
for	O
the	O
numerous	O
physics	O
modules	O
developed	O
for	O
the	O
code	O
that	O
go	O
beyond	O
gravity	O
and	O
ordinary	O
gas-dynamics	O
.	O
</s>
<s>
The	O
most	O
important	O
changes	O
lie	O
in	O
a	O
new	O
time	O
integration	O
model	O
,	O
a	O
new	O
tree-code	O
module	O
,	O
a	O
new	O
communication	O
scheme	O
for	O
gravitational	O
and	O
SPH	O
forces	O
,	O
a	O
new	O
domain	B-Algorithm
decomposition	I-Algorithm
strategy	O
,	O
a	O
novel	O
SPH	O
formulation	O
based	O
on	O
entropy	B-Algorithm
as	O
independent	O
variable	O
,	O
and	O
finally	O
,	O
in	O
the	O
addition	O
of	O
the	O
TreePM	O
functionality	O
.	O
</s>
