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- SUBROUTINE ZSQRT(AR, AI, BR, BI)
- C***BEGIN PROLOGUE ZSQRT
- C***REFER TO ZBESH,ZBESI,ZBESJ,ZBESK,ZBESY,ZAIRY,ZBIRY
- C
- C DOUBLE PRECISION COMPLEX SQUARE ROOT, B=CSQRT(A)
- C
- C***ROUTINES CALLED ZABS
- C***END PROLOGUE ZSQRT
- DOUBLE PRECISION AR, AI, BR, BI, ZM, DTHETA, DPI, DRT
- DOUBLE PRECISION ZABS
- DATA DRT , DPI / 7.071067811865475244008443621D-1,
- 1 3.141592653589793238462643383D+0/
- ZM = ZABS(COMPLEX(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
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