amos/zlog.f

   1       SUBROUTINE AZLOG(AR, AI, BR, BI, IERR)
   2 C***BEGIN PROLOGUE  AZLOG
   3 C***REFER TO  ZBESH,ZBESI,ZBESJ,ZBESK,ZBESY,ZAIRY,ZBIRY
   4 C
   5 C     DOUBLE PRECISION COMPLEX LOGARITHM B=CLOG(A)
   6 C     IERR=0,NORMAL RETURN      IERR=1, Z=CMPLX(0.0,0.0)
   7 C***ROUTINES CALLED  AZABS
   8 C***END PROLOGUE  AZLOG
   9       DOUBLE PRECISION AR, AI, BR, BI, ZM, DTHETA, DPI, DHPI
  10       DOUBLE PRECISION AZABS
  11       DATA DPI , DHPI  / 3.141592653589793238462643383D+0,
  12      1                   1.570796326794896619231321696D+0/
  13 C
  14       IERR=0
  15       IF (AR.EQ.0.0D+0) GO TO 10
  16       IF (AI.EQ.0.0D+0) GO TO 20
  17       DTHETA = DATAN(AI/AR)
  18       IF (DTHETA.LE.0.0D+0) GO TO 40
  19       IF (AR.LT.0.0D+0) DTHETA = DTHETA - DPI
  20       GO TO 50
  21    10 IF (AI.EQ.0.0D+0) GO TO 60
  22       BI = DHPI
  23       BR = DLOG(DABS(AI))
  24       IF (AI.LT.0.0D+0) BI = -BI
  25       RETURN
  26    20 IF (AR.GT.0.0D+0) GO TO 30
  27       BR = DLOG(DABS(AR))
  28       BI = DPI
  29       RETURN
  30    30 BR = DLOG(AR)
  31       BI = 0.0D+0
  32       RETURN
  33    40 IF (AR.LT.0.0D+0) DTHETA = DTHETA + DPI
  34    50 ZM = AZABS(AR,AI)
  35       BR = DLOG(ZM)
  36       BI = DTHETA
  37       RETURN
  38    60 CONTINUE
  39       IERR=1
  40       RETURN
  41       END