opclass for real[]

[ABHANG RANE <arane(at)indiana(dot)edu>]

Hi,
I have a column real[] in my table. I need to create a gist index on 
it. But the error is obvious as follows.

ERROR:  data type real[] has no default operator class for access 
method "gist"
HINT:  You must specify an operator class for the index or define a 
default operator class for the data type.

Is there a opclass defined in 8.2 or I have to create one. In either 
case can you please give a link for information on opclasses.

Thanks
Abhang