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SUBROUTINE ZWRSK(ZRR, ZRI, FNU, KODE, N, YR, YI, NZ, CWR, CWI,
* TOL, ELIM, ALIM)
C***BEGIN PROLOGUE ZWRSK
C***REFER TO ZBESI,ZBESK
C
C ZWRSK COMPUTES THE I BESSEL FUNCTION FOR RE(Z).GE.0.0 BY
C NORMALIZING THE I FUNCTION RATIOS FROM ZRATI BY THE WRONSKIAN
C
C***ROUTINES CALLED D1MACH,ZBKNU,ZRATI,AZABS
C***END PROLOGUE ZWRSK
C COMPLEX CINU,CSCL,CT,CW,C1,C2,RCT,ST,Y,ZR
DOUBLE PRECISION ACT, ACW, ALIM, ASCLE, CINUI, CINUR, CSCLR, CTI,
* CTR, CWI, CWR, C1I, C1R, C2I, C2R, ELIM, FNU, PTI, PTR, RACT,
* STI, STR, TOL, YI, YR, ZRI, ZRR, AZABS, D1MACH
INTEGER I, KODE, N, NW, NZ
DIMENSION YR(N), YI(N), CWR(2), CWI(2)
C-----------------------------------------------------------------------
C I(FNU+I-1,Z) BY BACKWARD RECURRENCE FOR RATIOS
C Y(I)=I(FNU+I,Z)/I(FNU+I-1,Z) FROM CRATI NORMALIZED BY THE
C WRONSKIAN WITH K(FNU,Z) AND K(FNU+1,Z) FROM CBKNU.
C-----------------------------------------------------------------------
NZ = 0
CALL ZBKNU(ZRR, ZRI, FNU, KODE, 2, CWR, CWI, NW, TOL, ELIM, ALIM)
IF (NW.NE.0) GO TO 50
CALL ZRATI(ZRR, ZRI, FNU, N, YR, YI, TOL)
C-----------------------------------------------------------------------
C RECUR FORWARD ON I(FNU+1,Z) = R(FNU,Z)*I(FNU,Z),
C R(FNU+J-1,Z)=Y(J), J=1,...,N
C-----------------------------------------------------------------------
CINUR = 1.0D0
CINUI = 0.0D0
IF (KODE.EQ.1) GO TO 10
CINUR = DCOS(ZRI)
CINUI = DSIN(ZRI)
10 CONTINUE
C-----------------------------------------------------------------------
C ON LOW EXPONENT MACHINES THE K FUNCTIONS CAN BE CLOSE TO BOTH
C THE UNDER AND OVERFLOW LIMITS AND THE NORMALIZATION MUST BE
C SCALED TO PREVENT OVER OR UNDERFLOW. CUOIK HAS DETERMINED THAT
C THE RESULT IS ON SCALE.
C-----------------------------------------------------------------------
ACW = AZABS(CWR(2),CWI(2))
ASCLE = 1.0D+3*D1MACH(1)/TOL
CSCLR = 1.0D0
IF (ACW.GT.ASCLE) GO TO 20
CSCLR = 1.0D0/TOL
GO TO 30
20 CONTINUE
ASCLE = 1.0D0/ASCLE
IF (ACW.LT.ASCLE) GO TO 30
CSCLR = TOL
30 CONTINUE
C1R = CWR(1)*CSCLR
C1I = CWI(1)*CSCLR
C2R = CWR(2)*CSCLR
C2I = CWI(2)*CSCLR
STR = YR(1)
STI = YI(1)
C-----------------------------------------------------------------------
C CINU=CINU*(CONJG(CT)/CABS(CT))*(1.0D0/CABS(CT) PREVENTS
C UNDER- OR OVERFLOW PREMATURELY BY SQUARING CABS(CT)
C-----------------------------------------------------------------------
PTR = STR*C1R - STI*C1I
PTI = STR*C1I + STI*C1R
PTR = PTR + C2R
PTI = PTI + C2I
CTR = ZRR*PTR - ZRI*PTI
CTI = ZRR*PTI + ZRI*PTR
ACT = AZABS(CTR,CTI)
RACT = 1.0D0/ACT
CTR = CTR*RACT
CTI = -CTI*RACT
PTR = CINUR*RACT
PTI = CINUI*RACT
CINUR = PTR*CTR - PTI*CTI
CINUI = PTR*CTI + PTI*CTR
YR(1) = CINUR*CSCLR
YI(1) = CINUI*CSCLR
IF (N.EQ.1) RETURN
DO 40 I=2,N
PTR = STR*CINUR - STI*CINUI
CINUI = STR*CINUI + STI*CINUR
CINUR = PTR
STR = YR(I)
STI = YI(I)
YR(I) = CINUR*CSCLR
YI(I) = CINUI*CSCLR
40 CONTINUE
RETURN
50 CONTINUE
NZ = -1
IF(NW.EQ.(-2)) NZ=-2
RETURN
END
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