Copy and paste this link:
http://journals.cambridge.org/action/displayAbstract?aid=1788564
Copy and paste this citation
ROLAND HILDEBRAND,
STEFANO MANCINI
and SIMONE SEVERINI
(2008).
Combinatorial laplacians and positivity under partial transpose. Mathematical Structures in Computer Science, 18
,
pp 205-219
doi:10.1017/S0960129508006634