+--------------------------------------------------------------------+
 |                                                                    |
 |                               SIMEPS                               |
 |                                                                    |
 +--------------------------------------------------------------------+

 MEANING: SIMEPS subroutine
 CONTEXT: NONMEM utility routine

 USAGE:
      USE SIZES, ONLY: DPSIZE,LVR
      REAL(KIND=DPSIZE):: EPS(LVR)
      CALL SIMEPS (EPS)

 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-ran-
 dom  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.
 (A level-two record has the same value of L2 and may also be called an |
 L2 record.)  (See L2).
 (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 Repetition_Variables),
 and  when  records of a level-two record are being repeated, with dif-
 ferent calls to SIMEPS with the  same  level-two  record,  the  values
 obtained are the last values stored in these variables 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 Simulation:_IETAOL_IEPSOL)

 So that simple simulation can be easily implemented  with  abbreviated
 code,  values  of epsilon are obtained by calls to SIMEPS occurring in
 the generated subroutine.  When the data are population 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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