You may define
MYETA1 = C11*ETA(1)
MYETA2 = C12*ETA(1)+C22*ETA(2)
MYETA3 = C23*ETA(2)+C33*ETA(3)
MYETA4 = C24*ETA(2)+C34*ETA(3)+C44*ETA(4)
with diagonal (and fixed to unit matrix) OMEGA matrix of ETA(1:4)
Then OMEGA for MYETA[1:4] matrix is
C11*C11
C11*C12 C12*C12+C22*C22
0 C22*C23 C23*C23+C33*C33
0 C22*C24 C23*C24+C33*C34 C24*C24+C34*C34+C44*C44
I am not sure whether it makes sense to go that far to get an extra 0 or
extra flexibility (relative to the band matrices with 1 or 3 zeros), but
technically, this is equivalent to the matrix that you need.
Another (simpler) option is to define
MYETA1 = ETA(1)
MYETA2 = ETA(2)
MYETA3 = ETA(3)
MYETA4 = ETA(4)+C24*ETA(2)
with the band matrix for ETAs:
Sw
C(w,x) Sx
0 C(x,y) Sy
0 0 C(y,z) Sz
The term C24*ETA(2) will add extra correlation (2-4) for MYETA matrix
that is forbidden by the band matrix for ETA(1:4).
Leonid
--------------------------------------
Leonid Gibiansky, Ph.D.
President, QuantPharm LLC
web: www.quantpharm.com
e-mail: LGibiansky at quantpharm.com
tel: (301) 767 5566
On 7/3/2015 9:58 AM, Gavin Jarvis wrote:
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: [email protected] <mailto:[email protected]>
Web: www.pdn.cam.ac.uk/staff/jarvis <http://www.pdn.cam.ac.uk/staff/jarvis>
Twitter: @GavinEJarvis
