SLATEC Routines --- DFEHL ---

*DECK DFEHL
      SUBROUTINE DFEHL (DF, NEQ, T, Y, H, YP, F1, F2, F3, F4, F5, YS,
     +   RPAR, IPAR)
C***BEGIN PROLOGUE  DFEHL
C***SUBSIDIARY
C***PURPOSE  Subsidiary to DDERKF
C***LIBRARY   SLATEC
C***TYPE      DOUBLE PRECISION (DEFEHL-S, DFEHL-D)
C***AUTHOR  Watts, H. A., (SNLA)
C***DESCRIPTION
C
C     Fehlberg Fourth-Fifth Order Runge-Kutta Method
C **********************************************************************
C
C    DFEHL integrates a system of NEQ first order
C    ordinary differential equations of the form
C               DU/DX = DF(X,U)
C    over one step when the vector Y(*) of initial values for U(*) and
C    the vector YP(*) of initial derivatives, satisfying  YP = DF(T,Y),
C    are given at the starting point X=T.
C
C    DFEHL advances the solution over the fixed step H and returns
C    the fifth order (sixth order accurate locally) solution
C    approximation at T+H in the array YS(*).
C    F1,---,F5 are arrays of dimension NEQ which are needed
C    for internal storage.
C    The formulas have been grouped to control loss of significance.
C    DFEHL should be called with an H not smaller than 13 units of
C    roundoff in T so that the various independent arguments can be
C    distinguished.
C
C    This subroutine has been written with all variables and statement
C    numbers entirely compatible with DRKFS. For greater efficiency,
C    the call to DFEHL can be replaced by the module beginning with
C    line 222 and extending to the last line just before the return
C    statement.
C
C **********************************************************************
C
C***SEE ALSO  DDERKF
C***ROUTINES CALLED  (NONE)
C***REVISION HISTORY  (YYMMDD)
C   820301  DATE WRITTEN
C   890831  Modified array declarations.  (WRB)
C   891214  Prologue converted to Version 4.0 format.  (BAB)
C   900328  Added TYPE section.  (WRB)
C   910722  Updated AUTHOR section.  (ALS)
C***END PROLOGUE  DFEHL