Parts 3 and 4 of the series on plane stress Drucker-Prager plasticity are now online. More to come soon.
Check out
http://www.parresianz.com/mechanics/plasticity/algorithm/plane-stress-drucker-prager-return-part-3/
and
http://www.parresianz.com/mechanics/plasticity/algorithm/plane-stress-drucker-prager-return-part-4/
-- Biswajit