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rk4.f
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2002-06-11
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35 lines
C
C PAGE 315-316: NUMERICAL MATHEMATICS AND COMPUTING, CHENEY/KINCAID, 1985
C
C FILE: RK4.FOR
C
C RUNGE-KUTTA METHOD OF ORDER 4 FOR SOLVING AN INITIAL VALUE PROBLEM (RK4,F)
C
EXTERNAL F
DATA T/1.0/, X/2.0/, H/7.8125E-3/, NSTEP/72/
CALL RK4(F,T,X,H,NSTEP)
STOP
END
FUNCTION F(T,X)
F = 2.0+(X-T-1.0)**2
RETURN
END
SUBROUTINE RK4(F,T,X,H,NSTEP)
PRINT 3,T,X
H2 = 0.5*H
START = T
DO 2 K = 1,NSTEP
F1 = H*F(T,X)
F2 = H*F(T + H2,X + 0.5*F1)
F3 = H*F(T + H2,X + 0.5*F2)
F4 = H*F(T + H,X + F3)
X = X + (F1 + F2 + F2 + F3 + F3 + F4)/6.0
T = START + H*REAL(K)
PRINT 3,T,X
2 CONTINUE
3 FORMAT(5X,2E22.14)
RETURN
END