<s>
Grammatical	B-Algorithm
evolution	I-Algorithm
(	O
GE	O
)	O
is	O
an	O
evolutionary	O
computation	O
and	O
,	O
more	O
specifically	O
,	O
a	O
genetic	B-Algorithm
programming	I-Algorithm
(	O
GP	O
)	O
technique	O
(	O
or	O
approach	O
)	O
pioneered	O
by	O
Conor	O
Ryan	O
,	O
JJ	O
Collins	O
and	O
Michael	O
O'Neill	O
in	O
1998	O
at	O
the	O
in	O
the	O
University	O
of	O
Limerick	O
.	O
</s>
<s>
In	O
most	O
published	O
work	O
on	O
GP	O
,	O
a	O
LISP-style	O
tree-structured	O
expression	O
is	O
directly	O
manipulated	O
,	O
whereas	O
GE	O
applies	O
genetic	O
operators	O
to	O
an	O
integer	O
string	O
,	O
subsequently	O
mapped	O
to	O
a	O
program	O
(	O
or	O
similar	O
)	O
through	O
the	O
use	O
of	O
a	O
grammar	O
,	O
which	O
is	O
typically	O
expressed	O
in	O
Backus	O
–	O
Naur	O
form	O
.	O
</s>
<s>
While	O
modern	O
Genetic	B-Algorithm
Programming	I-Algorithm
frameworks	O
support	O
typing	O
,	O
such	O
type-systems	O
have	O
limitations	O
that	O
Grammatical	B-Algorithm
Evolution	I-Algorithm
does	O
not	O
suffer	O
from	O
.	O
</s>
<s>
Observe	O
that	O
the	O
objects	O
GE	O
performs	O
search	O
on	O
are	O
the	O
same	O
as	O
those	O
used	O
in	O
genetic	B-Algorithm
algorithms	I-Algorithm
.	O
</s>
<s>
This	O
means	O
,	O
in	O
principle	O
,	O
that	O
any	O
existing	O
genetic	B-Algorithm
algorithm	I-Algorithm
package	O
,	O
such	O
as	O
the	O
popular	O
,	O
can	O
be	O
used	O
to	O
carry	O
out	O
the	O
search	O
,	O
and	O
a	O
developer	O
implementing	O
a	O
GE	O
system	O
need	O
only	O
worry	O
about	O
carrying	O
out	O
the	O
mapping	O
from	O
list	O
of	O
integers	O
to	O
program	O
tree	O
.	O
</s>
<s>
It	O
is	O
also	O
in	O
principle	O
possible	O
to	O
perform	O
the	O
search	O
using	O
some	O
other	O
method	O
,	O
such	O
as	O
particle	B-Algorithm
swarm	I-Algorithm
optimization	I-Algorithm
(	O
see	O
the	O
remark	O
below	O
)	O
;	O
the	O
modular	O
nature	O
of	O
GE	O
creates	O
many	O
opportunities	O
for	O
hybrids	O
as	O
the	O
problem	O
of	O
interest	O
to	O
be	O
solved	O
dictates	O
.	O
</s>
<s>
It	O
is	O
possible	O
to	O
structure	O
a	O
GE	O
grammar	O
that	O
for	O
a	O
given	O
function/terminal	O
set	O
is	O
equivalent	O
to	O
genetic	B-Algorithm
programming	I-Algorithm
.	O
</s>
<s>
Although	O
GE	O
was	O
originally	O
described	O
in	O
terms	O
of	O
using	O
an	O
Evolutionary	O
Algorithm	O
,	O
specifically	O
,	O
a	O
Genetic	B-Algorithm
Algorithm	I-Algorithm
,	O
other	O
variants	O
exist	O
.	O
</s>
<s>
For	O
example	O
,	O
GE	O
researchers	O
have	O
experimented	O
with	O
using	O
particle	B-Algorithm
swarm	I-Algorithm
optimization	I-Algorithm
to	O
carry	O
out	O
the	O
searching	O
instead	O
of	O
genetic	B-Algorithm
algorithms	I-Algorithm
with	O
results	O
comparable	O
to	O
that	O
of	O
normal	O
GE	O
;	O
this	O
is	O
referred	O
to	O
as	O
a	O
"	O
grammatical	O
swarm	O
"	O
;	O
using	O
only	O
the	O
basic	O
PSO	O
model	O
it	O
has	O
been	O
found	O
that	O
PSO	O
is	O
probably	O
equally	O
capable	O
of	O
carrying	O
out	O
the	O
search	O
process	O
in	O
GE	O
as	O
simple	O
genetic	B-Algorithm
algorithms	I-Algorithm
are	O
.	O
</s>
<s>
GE	O
was	O
originally	O
a	O
combination	O
of	O
the	O
linear	O
representation	O
as	O
used	O
by	O
the	O
Genetic	B-Algorithm
Algorithm	I-Algorithm
for	O
Developing	O
Software	O
(	O
GADS	O
)	O
and	O
Backus	O
Naur	O
Form	O
grammars	O
,	O
which	O
were	O
originally	O
used	O
in	O
tree-based	O
GP	O
by	O
Wong	O
and	O
Leung	O
in	O
1995	O
and	O
Whigham	O
in	O
1996	O
.	O
</s>
