SLATEC Routines --- DRKFS ---

*DECK DRKFS
      SUBROUTINE DRKFS (DF, NEQ, T, Y, TOUT, INFO, RTOL, ATOL, IDID, H,
     +   TOLFAC, YP, F1, F2, F3, F4, F5, YS, TOLD, DTSIGN, U26, RER,
     +   INIT, KSTEPS, KOP, IQUIT, STIFF, NONSTF, NTSTEP, NSTIFS, RPAR,
     +   IPAR)
C***BEGIN PROLOGUE  DRKFS
C***SUBSIDIARY
C***PURPOSE  Subsidiary to DDERKF
C***LIBRARY   SLATEC
C***TYPE      DOUBLE PRECISION (DERKFS-S, DRKFS-D)
C***AUTHOR  Watts, H. A., (SNLA)
C***DESCRIPTION
C
C     Fehlberg Fourth-Fifth Order Runge-Kutta Method
C **********************************************************************
C
C     DRKFS integrates a system of first order ordinary differential
C     equations as described in the comments for DDERKF .
C
C     The arrays YP,F1,F2,F3,F4,F5,and YS  (of length at least NEQ)
C     appear in the call list for variable dimensioning purposes.
C
C     The variables H,TOLFAC,TOLD,DTSIGN,U26,RER,INIT,KSTEPS,KOP,IQUIT,
C     STIFF,NONSTF,NTSTEP, and NSTIFS are used internally by the code
C     and appear in the call list to eliminate local retention of
C     variables between calls. Accordingly, these variables and the
C     array YP should not be altered.
C     Items of possible interest are
C         H  - An appropriate step size to be used for the next step
C         TOLFAC - Factor of change in the tolerances
C         YP - Derivative of solution vector at T
C         KSTEPS - Counter on the number of steps attempted
C
C **********************************************************************
C
C***SEE ALSO  DDERKF
C***ROUTINES CALLED  D1MACH, DFEHL, DHSTRT, DHVNRM, XERMSG
C***REVISION HISTORY  (YYMMDD)
C   820301  DATE WRITTEN
C   890531  Changed all specific intrinsics to generic.  (WRB)
C   890831  Modified array declarations.  (WRB)
C   891024  Changed references from DVNORM to DHVNRM.  (WRB)
C   891214  Prologue converted to Version 4.0 format.  (BAB)
C   900328  Added TYPE section.  (WRB)
C   900510  Convert XERRWV calls to XERMSG calls, change GOTOs to
C           IF-THEN-ELSEs.  (RWC)
C   910722  Updated AUTHOR section.  (ALS)
C***END PROLOGUE  DRKFS