dfehl.f
SUBROUTINE DFEHL (DF, NEQ, T, Y, H, YP, F1, F2, F3, F4, F5, YS,
+ RPAR, IPAR)
C***BEGIN PROLOGUE DFEHL
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Warning: this routine is not intended to be user-callable.
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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