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 |                                SIMEPS                           |
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 MEANING: SIMEPS subroutine
 CONTEXT: NONMEM utility routine

 USAGE:
 (If double precision is to be used):
 DOUBLE PRECISION EPS(LVR)
 (If single precision is to be used):
 REAL EPS(LVR)
  ...
 CALL SIMEPS (EPS)

 The value of LVR must  be  the  same  as  that  found  in  file  SIZES
 (See sizes).

 DISCUSSION:
 The NONMEM utility routine SIMEPS can be called  by  PRED  during  the
 simulation step, to obtain simulated epsilon values.  It may be called
 only when ICALL=4.

 Output argument:

  EPS An array  into  which  SIMEPS  stores  simulated  epsilon  values
      EPS(1),  EPS(2),  ....  The dimension of the array may be smaller
      than the maximum, e.g., it may equal the number  of  epsilons  in
      the problem.

 Simulated epsilon values arise  from  a  multivariate  normal  pseudo-
 random  distribution  with mean 0 and variance-covariance as specified
 for SIGMA.  With different calls to SIMEPS  with  different  level-two
 records,  new  and  different  simulated  epsilon values are obtained.
 (When the L2 data item is not defined, all data records are  level-two
 records,  and  so  different  data  records  are  different  level-two
 records.)  By default, with different calls to SIMEPS  with  the  same
 level-two  record,  the  same  simulated epsilon values are obtained -
 those obtained at the first  call  with  the  record.   (There  is  an
 advanced feature whereby records are "repeated" (See nmpr10), and when
 records of a level-two record are being repeated, with different calls
 to  SIMEPS with the same level-two record, the values obtained are the
 last values stored in nmprd7 when the record was previously passed  to
 PRED.)

 If, though, the NEW option is used with the first random source on the
 $SIMULATION  record, then each time SIMEPS is called (with the same or
 different level-two record), new and different  values  are  obtained.
 With  any particular call to SIMEPS, the effect of the NEW option can,
 though, be overridden; see nmpr11.

 So that simple simulation can be easily implemented  with  abbreviated
 code,  values  of epsilon are obtained by calls to SIMEPS occurring in
 the generated or NM-TRAN Library subroutine. When the data are popula-
 tion  data  and  the  Simulation Step is implemented, SIMEPS is called
 once with every call to PRED (or once at every call to ERROR if PREDPP
 is  used). These calls are implemented so that even if, initially, the
 Simulation Step is not implemented, the  NONMEM  executable  resulting
 from  using  an  abbreviated  code for PRED (or for ERROR if PREDPP is
 used) can be reused with a run implementing the Simulation Step.

 Additional calls to SIMEPS may appear in simulation blocks  of   $PRED
 and  $ERROR  abbreviated  code.  There is an analogous routine SIMETA.
 (See simeta).

REFERENCES: Guide IV Section III.B.13
REFERENCES: Guide V Section 12.4.8
REFERENCES: Guide VI Section IV.B.1, IV.B.2, Figure 10


  
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