Zeros in OMEGA matrix

Dear NMUsers I have a problem and hope someone might be able to help. In summary, is it possible for NONMEM to model an OMEGA matrix with four elements (W,X,Y,Z) such that two of the covariances are fixed to zero and the rest freely determined? I realise NONMEM can model BAND matrices, but I can't see how to fix just two covariances to zero. The final matrix structure I'm looking for would look something like. Sw C(w,x) Sx 0 C(x,y) Sy 0 C(x,z) C(y,z) Sz I hope that makes sense. If so, is it possible? Many thanks Gavin __________________________________________________ Dr Gavin E Jarvis MA(Cantab) MA PhD VetMB MRCVS University Lecturer in Veterinary Anatomy Department of Physiology, Development & Neuroscience Physiological Laboratory Downing Street Cambridge CB2 3EG Tel: +44 (0) 1223 333745 Fellow and College Lecturer in Pharmacology Tutor for Graduate Students Selwyn College Cambridge CB3 9DQ Tel: +44 (0) 1223 761303 Email: <mailto:[email protected]> [email protected] Web: http://www.pdn.cam.ac.uk/staff/jarvis www.pdn.cam.ac.uk/staff/jarvis Twitter: @GavinEJarvis