___________________________________________________________________
 |                                                                 |
 |                                $OMEGA                           |
 |_________________________________________________________________|

 MEANING: Supplies initial estimates for the NONMEM OMEGA Matrix
 CONTEXT: NM-TRAN Control Record

 USAGE:
 $OMEGA  [DIAGONAL(n)|BLOCK(n)|BLOCK(n) SAME|BLOCK SAME]
         [[value1]  [value2]  [value3] ... [FIXED]]

 SAMPLE:
 $OMEGA BLOCK(3)  6. .005 .3 .0002 .006 .4

 DISCUSSION:
 Gives initial estimates and constraints for elements of one or several
 blocks  of the OMEGA matrix, i.e., the matrix of variances and covari-
 ances of the eta variables in  the  statistical  model.   This  record
 should  appear  only  if the statistical model contains eta variables.
 Multiple $OMEGA records may be  used  to  define  multiple  blocks  of
 OMEGA.   The  order  of  the appearance of all blocks over all records
 corresponds to the order of the blocks in OMEGA.

 OPTIONS:

 There are three forms:

 1.   $OMEGA   [DIAGONAL(n)] [ v11 v22 v33 ... vnn ]

      This gives the initial estimates of the diagonal  elements  of  a
      diagonal block of OMEGA.  E.g.,
        $OMEGA .04 .12
        Initial estimate of variance of eta(1) = .04
        Initial estimate of variance of eta(2) = .12
      Each value may optionally be coded with one of the forms:
         init FIXED      (init FIXED)        (FIXED init)
      Option FIXED indicates that the variance is to be held  fixed  to
      the  given  initial estimate.  (When FIXED appears anywhere, then
      the block is  described  by  NONMEM  as  consisting  of  separate
      blocks, each of dimension one.)

 2.   $OMEGA BLOCK(n) [ v11 v21 v22 v31 v32 v33 ... vn1 vn2 ... vnn ]

      This gives the initial estimates of all the elements of a  nondi-
      agonal ("full") block of OMEGA.  E.g.,
        $OMEGA BLOCK(2) .04 .002 .12
        Initial estimate of variance of eta(1) = .04
        Initial estimate of covariance of eta(2), eta(1) = .002
        Initial estimate of variance of eta(2) = .12

      If FIXED appears anywhere among the list of  values,  the  entire
      block is fixed.

 3.   $OMEGA BLOCK(n) SAME

      This describes a block whose initial estimates, as well as  final
      estimates,  are constrained to be equal to those of the preceding
      block. Values may not be given. "(n)" may be omitted.

 If the values are omitted in forms 1 or 2, then  NONMEM  will  try  to
 obtain initial estimates.

REFERENCES: Guide I Section C.3.4.6, D.5.2, D.5.3
REFERENCES: Guide IV Section III.B.10, V.C.6
REFERENCES: Guide V Section 9.3


  
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