166 lines
4.9 KiB
Fortran
166 lines
4.9 KiB
Fortran
SUBROUTINE ZASYI(ZR, ZI, FNU, KODE, N, YR, YI, NZ, RL, TOL, ELIM,
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* ALIM)
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C***BEGIN PROLOGUE ZASYI
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C***REFER TO ZBESI,ZBESK
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C
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C ZASYI COMPUTES THE I BESSEL FUNCTION FOR REAL(Z).GE.0.0 BY
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C MEANS OF THE ASYMPTOTIC EXPANSION FOR LARGE CABS(Z) IN THE
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C REGION CABS(Z).GT.MAX(RL,FNU*FNU/2). NZ=0 IS A NORMAL RETURN.
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C NZ.LT.0 INDICATES AN OVERFLOW ON KODE=1.
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C
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C***ROUTINES CALLED D1MACH,ZABS,ZDIV,ZEXP,ZMLT,ZSQRT
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C***END PROLOGUE ZASYI
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C COMPLEX AK1,CK,CONE,CS1,CS2,CZ,CZERO,DK,EZ,P1,RZ,S2,Y,Z
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DOUBLE PRECISION AA, AEZ, AK, AK1I, AK1R, ALIM, ARG, ARM, ATOL,
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* AZ, BB, BK, CKI, CKR, CONEI, CONER, CS1I, CS1R, CS2I, CS2R, CZI,
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* CZR, DFNU, DKI, DKR, DNU2, ELIM, EZI, EZR, FDN, FNU, PI, P1I,
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* P1R, RAZ, RL, RTPI, RTR1, RZI, RZR, S, SGN, SQK, STI, STR, S2I,
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* S2R, TOL, TZI, TZR, YI, YR, ZEROI, ZEROR, ZI, ZR, D1MACH, ZABS
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INTEGER I, IB, IL, INU, J, JL, K, KODE, KODED, M, N, NN, NZ
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DIMENSION YR(N), YI(N)
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DATA PI, RTPI /3.14159265358979324D0 , 0.159154943091895336D0 /
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DATA ZEROR,ZEROI,CONER,CONEI / 0.0D0, 0.0D0, 1.0D0, 0.0D0 /
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C
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NZ = 0
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AZ = ZABS(ZR,ZI)
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ARM = 1.0D+3*D1MACH(1)
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RTR1 = DSQRT(ARM)
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IL = MIN0(2,N)
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DFNU = FNU + DBLE(FLOAT(N-IL))
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C-----------------------------------------------------------------------
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C OVERFLOW TEST
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C-----------------------------------------------------------------------
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RAZ = 1.0D0/AZ
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STR = ZR*RAZ
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STI = -ZI*RAZ
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AK1R = RTPI*STR*RAZ
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AK1I = RTPI*STI*RAZ
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CALL ZSQRT(AK1R, AK1I, AK1R, AK1I)
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CZR = ZR
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CZI = ZI
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IF (KODE.NE.2) GO TO 10
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CZR = ZEROR
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CZI = ZI
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10 CONTINUE
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IF (DABS(CZR).GT.ELIM) GO TO 100
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DNU2 = DFNU + DFNU
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KODED = 1
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IF ((DABS(CZR).GT.ALIM) .AND. (N.GT.2)) GO TO 20
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KODED = 0
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CALL ZEXP(CZR, CZI, STR, STI)
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CALL ZMLT(AK1R, AK1I, STR, STI, AK1R, AK1I)
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20 CONTINUE
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FDN = 0.0D0
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IF (DNU2.GT.RTR1) FDN = DNU2*DNU2
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EZR = ZR*8.0D0
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EZI = ZI*8.0D0
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C-----------------------------------------------------------------------
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C WHEN Z IS IMAGINARY, THE ERROR TEST MUST BE MADE RELATIVE TO THE
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C FIRST RECIPROCAL POWER SINCE THIS IS THE LEADING TERM OF THE
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C EXPANSION FOR THE IMAGINARY PART.
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C-----------------------------------------------------------------------
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AEZ = 8.0D0*AZ
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S = TOL/AEZ
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JL = INT(SNGL(RL+RL)) + 2
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P1R = ZEROR
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P1I = ZEROI
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IF (ZI.EQ.0.0D0) GO TO 30
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C-----------------------------------------------------------------------
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C CALCULATE EXP(PI*(0.5+FNU+N-IL)*I) TO MINIMIZE LOSSES OF
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C SIGNIFICANCE WHEN FNU OR N IS LARGE
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C-----------------------------------------------------------------------
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INU = INT(SNGL(FNU))
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ARG = (FNU-DBLE(FLOAT(INU)))*PI
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INU = INU + N - IL
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AK = -DSIN(ARG)
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BK = DCOS(ARG)
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IF (ZI.LT.0.0D0) BK = -BK
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P1R = AK
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P1I = BK
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IF (MOD(INU,2).EQ.0) GO TO 30
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P1R = -P1R
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P1I = -P1I
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30 CONTINUE
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DO 70 K=1,IL
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SQK = FDN - 1.0D0
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ATOL = S*DABS(SQK)
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SGN = 1.0D0
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CS1R = CONER
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CS1I = CONEI
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CS2R = CONER
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CS2I = CONEI
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CKR = CONER
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CKI = CONEI
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AK = 0.0D0
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AA = 1.0D0
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BB = AEZ
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DKR = EZR
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DKI = EZI
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DO 40 J=1,JL
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CALL ZDIV(CKR, CKI, DKR, DKI, STR, STI)
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CKR = STR*SQK
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CKI = STI*SQK
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CS2R = CS2R + CKR
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CS2I = CS2I + CKI
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SGN = -SGN
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CS1R = CS1R + CKR*SGN
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CS1I = CS1I + CKI*SGN
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DKR = DKR + EZR
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DKI = DKI + EZI
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AA = AA*DABS(SQK)/BB
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BB = BB + AEZ
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AK = AK + 8.0D0
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SQK = SQK - AK
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IF (AA.LE.ATOL) GO TO 50
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40 CONTINUE
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GO TO 110
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50 CONTINUE
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S2R = CS1R
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S2I = CS1I
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IF (ZR+ZR.GE.ELIM) GO TO 60
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TZR = ZR + ZR
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TZI = ZI + ZI
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CALL ZEXP(-TZR, -TZI, STR, STI)
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CALL ZMLT(STR, STI, P1R, P1I, STR, STI)
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CALL ZMLT(STR, STI, CS2R, CS2I, STR, STI)
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S2R = S2R + STR
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S2I = S2I + STI
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60 CONTINUE
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FDN = FDN + 8.0D0*DFNU + 4.0D0
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P1R = -P1R
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P1I = -P1I
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M = N - IL + K
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YR(M) = S2R*AK1R - S2I*AK1I
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YI(M) = S2R*AK1I + S2I*AK1R
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70 CONTINUE
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IF (N.LE.2) RETURN
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NN = N
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K = NN - 2
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AK = DBLE(FLOAT(K))
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STR = ZR*RAZ
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STI = -ZI*RAZ
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RZR = (STR+STR)*RAZ
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RZI = (STI+STI)*RAZ
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IB = 3
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DO 80 I=IB,NN
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YR(K) = (AK+FNU)*(RZR*YR(K+1)-RZI*YI(K+1)) + YR(K+2)
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YI(K) = (AK+FNU)*(RZR*YI(K+1)+RZI*YR(K+1)) + YI(K+2)
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AK = AK - 1.0D0
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K = K - 1
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80 CONTINUE
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IF (KODED.EQ.0) RETURN
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CALL ZEXP(CZR, CZI, CKR, CKI)
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DO 90 I=1,NN
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STR = YR(I)*CKR - YI(I)*CKI
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YI(I) = YR(I)*CKI + YI(I)*CKR
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YR(I) = STR
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90 CONTINUE
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RETURN
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100 CONTINUE
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NZ = -1
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RETURN
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110 CONTINUE
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NZ=-2
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RETURN
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END
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