Mercurial > octave-nkf

view libcruft/amos/xzsqrt.f @ 5018:1c65a8e44ef9 ss-2-1-59

Find changesets by keywords (author, files, the commit message), revision number or hash, or revset expression.
[project @ 2004-09-22 03:33:29 by jwe]
author jwe
date Wed, 22 Sep 2004 03:33:29 +0000
parents 8b0cb8f79fdc
children
line wrap: on
line source

      SUBROUTINE XZSQRT(AR, AI, BR, BI)
C***BEGIN PROLOGUE  XZSQRT
C***REFER TO  ZBESH,ZBESI,ZBESJ,ZBESK,ZBESY,ZAIRY,ZBIRY
C
C     DOUBLE PRECISION COMPLEX SQUARE ROOT, B=CSQRT(A)
C
C***ROUTINES CALLED  XZABS
C***END PROLOGUE  XZSQRT
      DOUBLE PRECISION AR, AI, BR, BI, ZM, DTHETA, DPI, DRT
      DOUBLE PRECISION XZABS
      DATA DRT , DPI / 7.071067811865475244008443621D-1,
     1                 3.141592653589793238462643383D+0/
      ZM = XZABS(AR,AI)
      ZM = DSQRT(ZM)
      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.GT.0.0D+0) GO TO 60
      IF (AI.LT.0.0D+0) GO TO 70
      BR = 0.0D+0
      BI = 0.0D+0
      RETURN
   20 IF (AR.GT.0.0D+0) GO TO 30
      BR = 0.0D+0
      BI = DSQRT(DABS(AR))
      RETURN
   30 BR = DSQRT(AR)
      BI = 0.0D+0
      RETURN
   40 IF (AR.LT.0.0D+0) DTHETA = DTHETA + DPI
   50 DTHETA = DTHETA*0.5D+0
      BR = ZM*DCOS(DTHETA)
      BI = ZM*DSIN(DTHETA)
      RETURN
   60 BR = ZM*DRT
      BI = ZM*DRT
      RETURN
   70 BR = ZM*DRT
      BI = -ZM*DRT
      RETURN
      END