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SUBROUTINE AZLOG(AR, AI, BR, BI, IERR)
C***BEGIN PROLOGUE AZLOG
C***REFER TO ZBESH,ZBESI,ZBESJ,ZBESK,ZBESY,ZAIRY,ZBIRY
C
C DOUBLE PRECISION COMPLEX LOGARITHM B=CLOG(A)
C IERR=0,NORMAL RETURN IERR=1, Z=CMPLX(0.0,0.0)
C***ROUTINES CALLED AZABS
C***END PROLOGUE AZLOG
DOUBLE PRECISION AR, AI, BR, BI, ZM, DTHETA, DPI, DHPI
DOUBLE PRECISION AZABS
DATA DPI , DHPI / 3.141592653589793238462643383D+0,
1 1.570796326794896619231321696D+0/
C
IERR=0
IF (AR.EQ.0.0D+0) GO TO 10
IF (AI.EQ.0.0D+0) GO TO 20
DTHETA = DATAN(AI/AR)
IF (DTHETA.LE.0.0D+0) GO TO 40
IF (AR.LT.0.0D+0) DTHETA = DTHETA - DPI
GO TO 50
10 IF (AI.EQ.0.0D+0) GO TO 60
BI = DHPI
BR = DLOG(DABS(AI))
IF (AI.LT.0.0D+0) BI = -BI
RETURN
20 IF (AR.GT.0.0D+0) GO TO 30
BR = DLOG(DABS(AR))
BI = DPI
RETURN
30 BR = DLOG(AR)
BI = 0.0D+0
RETURN
40 IF (AR.LT.0.0D+0) DTHETA = DTHETA + DPI
50 ZM = AZABS(AR,AI)
BR = DLOG(ZM)
BI = DTHETA
RETURN
60 CONTINUE
IERR=1
RETURN
END
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