Drawing graphs in cdec? can be done via the package graphviz?, which is open source (and in the apt repositories).
If cdec is run like this (genuine ex.):
cdec -c cdec.ini -w weights -i input3.txt --graphviz 2> graph
it outputs the graph info in a text format to STDERR alongside some running info, that must be cleaned from the files. STDOUT just echoes the input.
This can be transformed to a graph in graphviz like this:
dot -Goverlap=false -o graph.png -T png graph
The Goverlap=false makes sure it uses a big enough canvas to draw the entire graph, which (beware) easily gets very large.