___________________________________________________________________
 |                                                                 |
 |                             $COVARIANCE                         |
 |_________________________________________________________________|

 MEANING: Instructions for NONMEM Covariance Step
 CONTEXT: NM-TRAN Control Record

 USAGE:
 $COVARIANCE  [SPECIAL] [MATRIX=c] [PRINT=[E][R][S]
              [COMPRESS]
              [CONDITIONAL|UNCONDITIONAL]
              [NOSLOW|SLOW] [OMITTED]

 SAMPLE:
 $COVARIANCE

 DISCUSSION:
 Optional. Requests that the NONMEM  Covariance  Step  be  implemented.
 This  step  outputs:   standard  errors,  covariance  matrix,  inverse
 covariance matrix, and the correlation form of the covariance  matrix.
 May also be coded $COVR.

 OPTIONS:

 SPECIAL
      The special computation will be used in the Covariance Step  with
      a recursive PRED subroutine.  A recursive PRED subroutine is such
      that, with single-subject data, the PRED computation with a  data
      record depends on information passed to it with any of the previ-
                                                      ---
      ous data records.  This is the default when PREDPP is used.

 MATRIX=c
      Specifies that the covariance matrix will be different  from  the
      default  (R  sup  -1 S R sup -1).  MATRIX=R requests that 2 times
      the inverse R matrix be used.  MATRIX=S requests that 4 times the
      inverse  S  matrix be used.  (R and S are two matrices from  sta-
      tistical  theory,   the  Hessian   and   Cross-Product   Gradient
      matrices, respectively.)  MATRIX=R should not be used with option
      SPECIAL.

 PRINT=[E][R][S]
      Additional outputs will be  printed  besides  the  defaults.   E:
      print  the  eigenvalues  of the correlation matrix.  R: print the
      matrix .5*R.  S: print the matrix .25*S.  PRINT=R (or S)  is  not
      needed with MATRIX=R (or S).

 COMPRESS
      Covariance Step arrays are printed in compressed format, even  if
      their  size  is such that NONMEM would normally print them in the
      usual format.

 SLOW
      Requests a slower method of computation.  Required when either  a
      mixture  model  was  used along with CENTERING on the $ESTIMATION
      record, or NUMERICAL was used on the $ESTIMATION record.  If  not
      present,  the  option will be automatically supplied in these two
      cases.

 NOSLOW
      Requests a faster method of computation.   This  is  the  default
      (but see SLOW).

 CONDITIONAL
      The Covariance Step is implemented, but only when the  Estimation
      Step  terminates  successfully (in this run or in a run continued
      via $MSFI).  This is the default.

 UNCONDITIONAL                                                           |
      The Covariance Step is implemented even when the Estimation  Step  |
      terminates  unsuccessfully (in this run or in a run continued via  |
      $MSFI).                                                            |

 OMITTED
      The Covariance Step is not implemented.

REFERENCES: Guide IV Section III.B.15
REFERENCES: Guide V Section 9.4.2, 10.6


  
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