func.for

来自「给予DSMC的二维CFD模拟FORTRAN代码」· FOR 代码 · 共 68 行

*   GAM.FOR
*
      FUNCTION GAM(X)
*
*--calculates the Gamma function of X
*
      IMPLICIT DOUBLE PRECISION (A-H)
	IMPLICIT DOUBLE PRECISION (O-Z)

      A=1.
      Y=X
      IF (Y.LT.1.) THEN
        A=A/Y
      ELSE
50      Y=Y-1
        IF (Y.GE.1.) THEN
          A=A*Y
          GO TO 50
        END IF
      END IF
      GAM=A*(1.-0.5748646*Y+0.9512363*Y**2-0.6998588*Y**3+
     &    0.4245549*Y**4-0.1010678*Y**5)
      RETURN
      END
*   RF.FOR
*
      FUNCTION RF(IDUM)
*--generates a uniformly distributed random fraction between 0 and 1
*----IDUM will generally be 0, but negative values may be used to
*------re-initialize the seed
      SAVE MA,INEXT,INEXTP
      PARAMETER (MBIG=1000000000,MSEED=161803398,MZ=0,FAC=1.E-9)
      DIMENSION MA(55)
      DATA IFF/0/
      IF (IDUM.LT.0.OR.IFF.EQ.0) THEN
        IFF=1
        MJ=MSEED-IABS(IDUM)
        MJ=MOD(MJ,MBIG)
        MA(55)=MJ
        MK=1
        DO 50 I=1,54
          II=MOD(21*I,55)
          MA(II)=MK
          MK=MJ-MK
          IF (MK.LT.MZ) MK=MK+MBIG
          MJ=MA(II)
50      CONTINUE
        DO 100 K=1,4
          DO 60 I=1,55
            MA(I)=MA(I)-MA(1+MOD(I+30,55))
            IF (MA(I).LT.MZ) MA(I)=MA(I)+MBIG
60        CONTINUE
100     CONTINUE
        INEXT=0
        INEXTP=31
      END IF
200   INEXT=INEXT+1
      IF (INEXT.EQ.56) INEXT=1
      INEXTP=INEXTP+1
      IF (INEXTP.EQ.56) INEXTP=1
      MJ=MA(INEXT)-MA(INEXTP)
      IF (MJ.LT.MZ) MJ=MJ+MBIG
      MA(INEXT)=MJ
      RF=MJ*FAC
      IF (RF.GT.1.E-8.AND.RF.LT.0.99999999) RETURN
      GO TO 200
      END