http://qs321.pair.com?node_id=245271

in reply to Re: Re: XML probabilistic trees

So, you've got something like:

```%nodes=( root => { parents => [],
probs => [0.01]}, # P(root)
some => { parents => ['n1'],
probs => [0.74,0.21]}, # P(some|!root), P(some|root
+)
other =>{ parents => ['root','n1'],
probs => [0.12,0.24,   # P(other|!root,!some), P(ot
+her|!root,some)
0.81,0.18]}, # P(other|root,!some), P(oth
+er|root,some)
);

I choose an array to represent the join probabilities because I thought it would be the easiest way. You get the entry you need with something like:

```# the state you start from
%state=(root=>1,some=>0);
# let's get P(other|root,!some)
\$i=0;
for @{\$nodes{other}{parents}} {
\$i=(\$i<<2)+\$state{\$_} # this is a simple encoding. Just use the same
+for updating and accessing
}
\$prob=\$nodes{other}{probs}[\$i];

When you have trained your network, you can dump it using XML::Simple:

```use XML::Simple;
print XMLout(\%nodes);

I think this code should work as well with full-fledged belief networks, since I'm using names to refer to nodes, instead of nesting their representation in the XML tree.

```--
dakkar - Mobilis in mobile
```

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Re: Re: Re: Re: XML probabilistic trees
by matth (Monk) on Mar 25, 2003 at 10:13 UTC
Out of interest. Can anyone tell me why, when I print out with the command:
```

print XMLout(\%nodes);
```--