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- *DECK ZLOG
- SUBROUTINE ZLOG (AR, AI, BR, BI, IERR)
- C***BEGIN PROLOGUE ZLOG
- C***SUBSIDIARY
- C***PURPOSE Subsidiary to ZBESH, ZBESI, ZBESJ, ZBESK, ZBESY, ZAIRY and
- C ZBIRY
- C***LIBRARY SLATEC
- C***TYPE ALL (ZLOG-A)
- C***AUTHOR Amos, D. E., (SNL)
- C***DESCRIPTION
- C
- C DOUBLE PRECISION COMPLEX LOGARITHM B=CLOG(A)
- C IERR=0,NORMAL RETURN IERR=1, Z=CMPLX(0.0,0.0)
- C***SEE ALSO ZAIRY, ZBESH, ZBESI, ZBESJ, ZBESK, ZBESY, ZBIRY
- C***ROUTINES CALLED ZABS
- C***REVISION HISTORY (YYMMDD)
- C 830501 DATE WRITTEN
- C 910415 Prologue converted to Version 4.0 format. (BAB)
- C***END PROLOGUE ZLOG
- DOUBLE PRECISION AR, AI, BR, BI, ZM, DTHETA, DPI, DHPI
- DOUBLE PRECISION ZABS
- INTEGER IERR
- EXTERNAL ZABS
- DATA DPI , DHPI / 3.141592653589793238462643383D+0,
- 1 1.570796326794896619231321696D+0/
- C***FIRST EXECUTABLE STATEMENT ZLOG
- 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 = LOG(ABS(AI))
- IF (AI.LT.0.0D+0) BI = -BI
- RETURN
- 20 IF (AR.GT.0.0D+0) GO TO 30
- BR = LOG(ABS(AR))
- BI = DPI
- RETURN
- 30 BR = LOG(AR)
- BI = 0.0D+0
- RETURN
- 40 IF (AR.LT.0.0D+0) DTHETA = DTHETA + DPI
- 50 ZM = ZABS(AR,AI)
- BR = LOG(ZM)
- BI = DTHETA
- RETURN
- 60 CONTINUE
- IERR=1
- RETURN
- END
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