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 MEANING: DES subroutine
 CONTEXT: User-supplied subroutine; for use with PREDPP's ADVAN 6, 8, 9

 USAGE:

 SUBROUTINE DES (A,P,T,DADT,IR,DA,DP,DT)
 INTEGER IR
 DIMENSION A(*),P(*),DADT(*),DA(IR,*),DP(IR,*),DT(*)
 (If double precision is to be used):
 DOUBLE PRECISION A,P,T,DADT,DA,DP,DT
 (If single precision is to be used):
 REAL A,P,T,DADT,DA,DP,DT

 DISCUSSION:
 The DES subroutine is called by PREDPP to evaluate right-sides of dif-
 ferential equations.

 Input argument:

 A(n) The amount in the nth compartment at time T.

 P(n) The value of the nth PK parameter.

 T    Time. T takes values continuously over an integration interval.

 Output argument:

 DADT(n)
      The derivative with respect to T of the nth compartment's amount.
      It  is important to note that PREDPP itself adds in the rates for
      any infusions that may be active.

      It is possible to introduce drug into a compartment  by  explicit
      terms  in  a  differential  equation,  rather than by PREDPP dose
      event records.  Drug introduced in this manner is not included by
      PREDPP  in  the  computation of the output compartment.  Specifi-
      cally, the amount in the output compartment may be thought of  as
      being  calculated  by  summing  all relevant doses from the INPUT
      file (i.e., those that precede the time of  the  present  record,
      accounting  for bioavailability), subtracting all amounts present
      in compartments other than the output compartment, and then  mul-
      tiplying the result by the output fraction parameter.

      For example, suppose differential equations were used for ADVAN2,
      rather than the analytic solution.  They would be:
      DADT(1)=-P(3)*A(1)
      DADT(2)= P(3)*A(1)-P(1)*A(2)

 DA(n,j)
      The derivative of DADT(n) with respect to  A(j).  Continuing  the
      above example,
      DA(1,1)=-P(3)
      DA(2,1)= P(3)
      DA(2,2)=-P(1)

 DP(n,j)
      The derivative of DADT(n) with respect to  P(j).  Continuing  the
      above example,
      DP(1,3)=-A(1)
      DP(2,3)= A(1)
      DP(2,1)=-A(2)

 DT(n)
      The derivative of DADT(n) with respect to T.

 The format of arrays DA, DP, DT described above is called  "full  for-
 mat".   Alternately,  compact  format may be used (See prdde1).  It is
 the default format for these arrays.  A description of compact  format
 is beyond the scope of this document.

 Also see NONMEM read-only commons (of  the  form  ROCMn),  NONMEM-PRED
 commons  (of  the  form NMPRDn), PREDPP read-only commons (of the form
 PROCMn), and PREDPP common PRDDE1.

REFERENCES: Guide IV Section V.C.7
REFERENCES: Guide VI Section VI.C


  
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