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decuslib20-02
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decus/20-0026/rk2.doc
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SUBROUTINE RK2
PURPOSE
INTEGRATES A FIRST ORDER DIFFERENTIAL EQUATION
DY/DX=FUN(X,Y) AND PRODUCES A TABLE OF INTEGRATED VALUES
USAGE
CALL RK2(FUN,H,XI,YI,K,N,VEC)
DESCRIPTION OF PARAMETERS
FUN-USER-SUPPLIED FUNCTION SUBPROGRAM WITH ARGUMENTS X,Y
WHICH GIVES DY/DX
H -STEP SIZE
XI -INITIAL VALUE OF X
YI -INITIAL VALUE OF Y WHERE YI=Y(XI)
K -THE INTERVAL AT WHICH COMPUTED VALUES ARE TO BE STORED
N -THE NUMBER OF VALUES TO BE STORED
VEC-THE RESULTANT VECTOR OF LENGTH N IN WHICH COMPUTED
VALUES OF Y ARE TO BE STORED
REMARKS
NONE
SUBROUTINES AND FUNCTION SUBPROGRAMS REQUIRED
FUN - USER-SUPPLIED FUNCTION SUBPROGRAM FOR DY/DX
CALLING PROGRAM MUST HAVE FORTRAN EXTERNAL STATEMENT
CONTAINING NAMES OF FUNCTION SUBPROGRAMS LISTED IN CALL TO
RK2
METHOD
FOURTH ORDER RUNGE-KUTTA INTEGRATION ON A RECURSIVE BASIS AS
SHOWN IN F.B. HILDEBRAND, 'INTRODUCTION TO NUMERICAL
ANALYSIS', MCGRAW-HILL, NEW YORK, 1956